Make sure branch-heads is configured whenever requested.

This allows the branch-heads to be pulled even if not configured on the
original clone.

Review URL: https://codereview.chromium.org/13951009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@194382 0039d316-1c4b-4281-b951-d872f2087c98
naive nohooks