codereview: fix hg change on Windows
codereview: fix hg change on Windows

hg change fails on Windows with 'No valid patches found in output from hg diff'.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4006043

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go