os: fixed PathListSeparator to ';' for windows.

Fixed issue 1992

R=golang-dev, alex.brainman
CC=golang-dev
https://golang.org/cl/4661047

src/pkg/os/path_windows.go

@@ -6,7 +6,7 @@ package os
 
 const (
 	PathSeparator     = '\\' // OS-specific path separator
-	PathListSeparator = ':'  // OS-specific path list separator
+	PathListSeparator = ';'  // OS-specific path list separator
 )
 
 // IsPathSeparator returns true if c is a directory separator character.