Retries unlock when process is still up but config server has gone down,
in case of errors during locking and unlocking. Also allows testing
of locks already held.
In general, the current distributed lock is susceptible to time skew in config servers and mongos clients. This update
uses an algorithm that checks for time skew, as well as providing some more robust tests to make sure a distributed
lock cannot be forced prematurely. Some documentation on the website, currently hidden from non-10gen, gives more
info.
