os: New Open API.
We replace the current Open with:
OpenFile(name, flag, perm) // same as old Open
Open(name) // same as old Open(name, O_RDONLY, 0)
Create(name) // same as old Open(name, O_RDWR|O_TRUNC|O_CREAT, 0666)

This CL includes a gofix module and full code updates: all.bash passes.
(There may be a few comments I missed.)

The interesting packages are:
        gofix
        os
Everything else is automatically generated except for hand tweaks to:
        src/pkg/io/ioutil/ioutil.go
        src/pkg/io/ioutil/tempfile.go
        src/pkg/crypto/tls/generate_cert.go
        src/cmd/goyacc/goyacc.go
        src/cmd/goyacc/units.y

R=golang-dev, bradfitzwork, rsc, r2
CC=golang-dev
https://golang.org/cl/4357052
diff --git a/src/pkg/os/sys_plan9.go b/src/pkg/os/sys_plan9.go
index ac44445..f6af28b 100644
--- a/src/pkg/os/sys_plan9.go
+++ b/src/pkg/os/sys_plan9.go
@@ -8,7 +8,7 @@
 
 
 func Hostname() (name string, err Error) {
-	f, err := Open("#c/sysname", O_RDONLY, 0)
+	f, err := Open("#c/sysname")
 	if err != nil {
 		return "", err
 	}