For a repo without push, update to branch instead of 000000000000

locale-inspector currently updates to an empty repo via revision 000000000000.
This was for historic reruns, mostly, but it's hurting us in practice today
when we fork repos on the hg server.

Instead, we should just update to the hg branch specified, 'default' these days.

--HG--
extra : amend_source : 19eeb3c69b9485b9de22cec719fd04294d34f228