net, os, syscall: delete os.EPLAN9

Also fixes plan9 cross-build.

R=rsc, r
CC=golang-dev
https://golang.org/cl/5675073
diff --git a/src/pkg/net/file_plan9.go b/src/pkg/net/file_plan9.go
index 06d7cc8..04f7ee0 100644
--- a/src/pkg/net/file_plan9.go
+++ b/src/pkg/net/file_plan9.go
@@ -6,6 +6,7 @@
 
 import (
 	"os"
+	"syscall"
 )
 
 // FileConn returns a copy of the network connection corresponding to
@@ -13,7 +14,7 @@
 // finished.  Closing c does not affect f, and closing f does not
 // affect c.
 func FileConn(f *os.File) (c Conn, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // FileListener returns a copy of the network listener corresponding
@@ -21,7 +22,7 @@
 // when finished.  Closing c does not affect l, and closing l does not
 // affect c.
 func FileListener(f *os.File) (l Listener, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // FilePacketConn returns a copy of the packet network connection
@@ -29,5 +30,5 @@
 // responsibility to close f when finished.  Closing c does not affect
 // f, and closing f does not affect c.
 func FilePacketConn(f *os.File) (c PacketConn, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
diff --git a/src/pkg/net/iprawsock_plan9.go b/src/pkg/net/iprawsock_plan9.go
index 382a4402..43719fc9 100644
--- a/src/pkg/net/iprawsock_plan9.go
+++ b/src/pkg/net/iprawsock_plan9.go
@@ -7,7 +7,7 @@
 package net
 
 import (
-	"os"
+	"syscall"
 	"time"
 )
 
@@ -17,34 +17,34 @@
 
 // SetDeadline implements the Conn SetDeadline method.
 func (c *IPConn) SetDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetReadDeadline implements the Conn SetReadDeadline method.
 func (c *IPConn) SetReadDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
 func (c *IPConn) SetWriteDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // Implementation of the Conn interface - see Conn for documentation.
 
 // Read implements the Conn Read method.
 func (c *IPConn) Read(b []byte) (int, error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // Write implements the Conn Write method.
 func (c *IPConn) Write(b []byte) (int, error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // Close closes the IP connection.
 func (c *IPConn) Close() error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // LocalAddr returns the local network address.
@@ -67,12 +67,12 @@
 // Timeout() == true after a fixed time limit; see SetDeadline and
 // SetReadDeadline.
 func (c *IPConn) ReadFromIP(b []byte) (int, *IPAddr, error) {
-	return 0, nil, os.EPLAN9
+	return 0, nil, syscall.EPLAN9
 }
 
 // ReadFrom implements the PacketConn ReadFrom method.
 func (c *IPConn) ReadFrom(b []byte) (int, Addr, error) {
-	return 0, nil, os.EPLAN9
+	return 0, nil, syscall.EPLAN9
 }
 
 // WriteToIP writes a IP packet to addr via c, copying the payload from b.
@@ -82,18 +82,18 @@
 // see SetDeadline and SetWriteDeadline.
 // On packet-oriented connections, write timeouts are rare.
 func (c *IPConn) WriteToIP(b []byte, addr *IPAddr) (int, error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // WriteTo implements the PacketConn WriteTo method.
 func (c *IPConn) WriteTo(b []byte, addr Addr) (int, error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // DialIP connects to the remote address raddr on the network protocol netProto,
 // which must be "ip", "ip4", or "ip6" followed by a colon and a protocol number or name.
 func DialIP(netProto string, laddr, raddr *IPAddr) (*IPConn, error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // ListenIP listens for incoming IP packets addressed to the
@@ -101,5 +101,5 @@
 // and WriteTo methods can be used to receive and send IP
 // packets with per-packet addressing.
 func ListenIP(netProto string, laddr *IPAddr) (*IPConn, error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
diff --git a/src/pkg/net/ipsock_plan9.go b/src/pkg/net/ipsock_plan9.go
index 385da03..eab0bf3 100644
--- a/src/pkg/net/ipsock_plan9.go
+++ b/src/pkg/net/ipsock_plan9.go
@@ -10,6 +10,7 @@
 	"errors"
 	"io"
 	"os"
+	"syscall"
 	"time"
 )
 
@@ -148,17 +149,17 @@
 
 // SetDeadline implements the Conn SetDeadline method.
 func (c *plan9Conn) SetDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetReadDeadline implements the Conn SetReadDeadline method.
 func (c *plan9Conn) SetReadDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
 func (c *plan9Conn) SetWriteDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 func startPlan9(net string, addr Addr) (ctl *os.File, dest, proto, name string, err error) {
diff --git a/src/pkg/net/lookup_plan9.go b/src/pkg/net/lookup_plan9.go
index c0bb922..b08a9fb 100644
--- a/src/pkg/net/lookup_plan9.go
+++ b/src/pkg/net/lookup_plan9.go
@@ -7,6 +7,7 @@
 import (
 	"errors"
 	"os"
+	"syscall"
 )
 
 func query(filename, query string, bufSize int) (res []string, err error) {
@@ -71,7 +72,7 @@
 
 func lookupProtocol(name string) (proto int, err error) {
 	// TODO: Implement this
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 func lookupHost(host string) (addrs []string, err error) {
diff --git a/src/pkg/net/tcpsock_plan9.go b/src/pkg/net/tcpsock_plan9.go
index be89e53..35f5696 100644
--- a/src/pkg/net/tcpsock_plan9.go
+++ b/src/pkg/net/tcpsock_plan9.go
@@ -7,7 +7,7 @@
 package net
 
 import (
-	"os"
+	"syscall"
 	"time"
 )
 
@@ -19,17 +19,17 @@
 
 // SetDeadline implements the Conn SetDeadline method.
 func (c *TCPConn) SetDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetReadDeadline implements the Conn SetReadDeadline method.
 func (c *TCPConn) SetReadDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
 func (c *TCPConn) SetWriteDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // CloseRead shuts down the reading side of the TCP connection.
@@ -38,7 +38,7 @@
 	if !c.ok() {
 		return syscall.EINVAL
 	}
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // CloseWrite shuts down the writing side of the TCP connection.
@@ -47,7 +47,7 @@
 	if !c.ok() {
 		return syscall.EINVAL
 	}
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // DialTCP connects to the remote address raddr on the network net,
diff --git a/src/pkg/net/udpsock_plan9.go b/src/pkg/net/udpsock_plan9.go
index d1f83d3..4f298a4 100644
--- a/src/pkg/net/udpsock_plan9.go
+++ b/src/pkg/net/udpsock_plan9.go
@@ -9,6 +9,7 @@
 import (
 	"errors"
 	"os"
+	"syscall"
 	"time"
 )
 
@@ -20,17 +21,17 @@
 
 // SetDeadline implements the Conn SetDeadline method.
 func (c *UDPConn) SetDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetReadDeadline implements the Conn SetReadDeadline method.
 func (c *UDPConn) SetReadDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
 func (c *UDPConn) SetWriteDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // UDP-specific methods.
@@ -191,5 +192,5 @@
 // the interface to join.  ListenMulticastUDP uses default
 // multicast interface if ifi is nil.
 func ListenMulticastUDP(net string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
diff --git a/src/pkg/net/unixsock_plan9.go b/src/pkg/net/unixsock_plan9.go
index 1d9d757..7b4ae6b 100644
--- a/src/pkg/net/unixsock_plan9.go
+++ b/src/pkg/net/unixsock_plan9.go
@@ -7,7 +7,7 @@
 package net
 
 import (
-	"os"
+	"syscall"
 	"time"
 )
 
@@ -19,17 +19,17 @@
 
 // Read implements the Conn Read method.
 func (c *UnixConn) Read(b []byte) (n int, err error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // Write implements the Conn Write method.
 func (c *UnixConn) Write(b []byte) (n int, err error) {
-	return 0, os.EPLAN9
+	return 0, syscall.EPLAN9
 }
 
 // Close closes the Unix domain connection.
 func (c *UnixConn) Close() error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // LocalAddr returns the local network address, a *UnixAddr.
@@ -47,28 +47,28 @@
 
 // SetDeadline implements the Conn SetDeadline method.
 func (c *UnixConn) SetDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetReadDeadline implements the Conn SetReadDeadline method.
 func (c *UnixConn) SetReadDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
 func (c *UnixConn) SetWriteDeadline(t time.Time) error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // ReadFrom implements the PacketConn ReadFrom method.
 func (c *UnixConn) ReadFrom(b []byte) (n int, addr Addr, err error) {
-	err = os.EPLAN9
+	err = syscall.EPLAN9
 	return
 }
 
 // WriteTo implements the PacketConn WriteTo method.
 func (c *UnixConn) WriteTo(b []byte, addr Addr) (n int, err error) {
-	err = os.EPLAN9
+	err = syscall.EPLAN9
 	return
 }
 
@@ -76,7 +76,7 @@
 // which must be "unix" or "unixgram".  If laddr is not nil, it is used
 // as the local address for the connection.
 func DialUnix(net string, laddr, raddr *UnixAddr) (c *UnixConn, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // UnixListener is a Unix domain socket listener.
@@ -87,19 +87,19 @@
 // ListenUnix announces on the Unix domain socket laddr and returns a Unix listener.
 // Net must be "unix" (stream sockets).
 func ListenUnix(net string, laddr *UnixAddr) (l *UnixListener, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // Accept implements the Accept method in the Listener interface;
 // it waits for the next call and returns a generic Conn.
 func (l *UnixListener) Accept() (c Conn, err error) {
-	return nil, os.EPLAN9
+	return nil, syscall.EPLAN9
 }
 
 // Close stops listening on the Unix address.
 // Already accepted connections are not closed.
 func (l *UnixListener) Close() error {
-	return os.EPLAN9
+	return syscall.EPLAN9
 }
 
 // Addr returns the listener's network address.