single argument panic

note that sortmain.go has been run through hg gofmt;
only the formatting of the day initializers changed.
i'm happy to revert that formatting if you'd prefer.

stop on error in doc/progs/run

R=r
CC=golang-dev
https://golang.org/cl/850041
diff --git a/src/pkg/net/unixsock.go b/src/pkg/net/unixsock.go
index 727b99f..daf71c0 100644
--- a/src/pkg/net/unixsock.go
+++ b/src/pkg/net/unixsock.go
@@ -25,7 +25,7 @@
 	var la, ra syscall.Sockaddr
 	switch mode {
 	default:
-		panic("unixSocket", mode)
+		panic("unixSocket mode " + mode)
 
 	case "dial":
 		if laddr != nil {