R1:59922b78b9bc

Make Phabricator clone bare git repositories

Summary:
This doesn't really impact anything very much, but is a little cleaner than cloning repositories with a working copy. It's somewhat important for allowing pushes, because you can't push to a checked-out branch.

Mercurial has a similar option (`--noupdate`) but leave that alone for now.

The origin stuff was mostly for sanity/explicitness purposes -- I believe it's safe to remove in all non-ridiculous cases. Git fails with it in bare repositories (it…