flag: export commandLine, the previously internal default FlagSet
s/commandLine/CommandLine/g

Fixes #4209.

R=golang-dev, dsymonds, bradfitz
CC=golang-dev
https://golang.org/cl/12587043
diff --git a/src/pkg/flag/export_test.go b/src/pkg/flag/export_test.go
index 7b19080..56cda58 100644
--- a/src/pkg/flag/export_test.go
+++ b/src/pkg/flag/export_test.go
@@ -12,11 +12,6 @@
 // After calling ResetForTesting, parse errors in flag handling will not
 // exit the program.
 func ResetForTesting(usage func()) {
-	commandLine = NewFlagSet(os.Args[0], ContinueOnError)
+	CommandLine = NewFlagSet(os.Args[0], ContinueOnError)
 	Usage = usage
 }
-
-// CommandLine returns the default FlagSet.
-func CommandLine() *FlagSet {
-	return commandLine
-}