Synchronize access to write batches and iterators.
Synchronize access to write batches and iterators.

Just your average mutexes to ensure that we only have one thread
manipulating the objects at any given time. In general I don't
expect these to stray out of a single Erlang process so there
shouldn't be much lock contention.

kevsmith/erleveldb,kevsmith/erleveldb,kevsmith/erleveldb