Code review comment for lp:~mkanat/loggerhead/synchronize-lru_cache

Okay, John is right--the bug is not fixed. I just ran into it on bzr.mozilla.org again.

For loggerhead, a quick workaround is to make the lock global instead of a per-instance item.

We do have cleanups, and I suppose it's possible for us to be updating an existing branch with a new cache, right? So I think we'll need this lock in loggerhead anyway.