codereview: extra repo sanity check
codereview: extra repo sanity check

Also work around Mercurial issue 3023.

If anyone has local changes in their repo (due to
patch queues or whatever) stop them from leaking
into the main repository.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5144043
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go