Avoid locks in the master repo just to clone it.

Expose the checks done to 'ensure' that a given path is a valid
bare repository. This allows this check to be done without needing
to instantiate a GitRepository, removing the need for a lock on it.

This should make per-user clones more efficient, while containing
the same level of safety checks.

Change-Id: I138a2f5ce1ef193b41ccc54b762b2a7760ad2d27
Fix #1626: Reduce the poll frequency to 30s.

This reduces the load on the server (30s should be short enough
to remain useful) and will allow for longer KeepAlives if we want.
Also reduce the retry count as the server isn't really likely to
recover in the few seconds between retries.

Change-Id: I0c6ed7a778338ae85263a40f4dcec73940e325b0
Bump pyenv to make comp/dev mode work

Fixing trac bug #1640