Concurrent session access in Jackrabbit's LockManager timeout handler

We often see issues due to session write concurrency when unlocking and refreshing locks. Jackrabbit pro-actively times out locks on a dedicated thread. When timeout and unlocks or refreshes of locks happen simultaneously you see failures due to concurrent session access. Since we now have our own just-in-time unlocking logic in place, these pro-active unlocks seem not to be necessary any more. We can disable it in our patched Jackrabbit.