git-codereview: set x.mailed tag to mailed commit instead of HEAD

Currently, git codereview mail sets the <branch>.mailed tag to the
current HEAD, even if mail was given a different hash on the command
line.

Fix this to set the <branch>.mailed tag to the commit hash that was
sent to Gerrit.

Change-Id: Ie0aa1512610121ba508b6668f21b50a0ca1c70f8
Reviewed-on: https://go-review.googlesource.com/7731
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>
1 file changed