This cl ensures that gclient enforces sane revision overrides and
onfiguration when running a revert, just like it does on a normal sync/update.

R=iannucci@chromium.org
BUG=420919

Review URL: https://codereview.chromium.org/1160113003.

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295571 0039d316-1c4b-4281-b951-d872f2087c98