git-review: add change -q quick mode, to not edit existing commit message

If -q is given and there's an existing commit, git-review skips the editor session.
If you've made a tiny change, then all you have to do is:

	git add foo.go
	git change -q

to update the commit.

Change-Id: I38b1f71a27d0953648eeff56a4024abc24f46fe2
Reviewed-on: https://go-review.googlesource.com/1443
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/git-review/change.go b/git-review/change.go
index 9e5f1d5..d1a21c5 100644
--- a/git-review/change.go
+++ b/git-review/change.go
@@ -10,7 +10,10 @@
 	"strings"
 )
 
+var changeQuick bool
+
 func change(args []string) {
+	flags.BoolVar(&changeQuick, "q", false, "do not edit commit msg when updating commit")
 	flags.Parse(args)
 	if len(flags.Args()) > 1 {
 		fmt.Fprintf(os.Stderr, "Usage: %s change %s [branch]\n", os.Args[0], globalFlags)
@@ -57,6 +60,9 @@
 	args := []string{"commit", "-q", "--allow-empty"}
 	if amend {
 		args = append(args, "--amend")
+		if changeQuick {
+			args = append(args, "--no-edit")
+		}
 	}
 	if testCommitMsg != "" {
 		args = append(args, "-m", testCommitMsg)