pruneLocks could create deadlocked transactions on PostgreSQL if multiple locks expired and pruneLocks is called by multiple instances. Also adds some logging.
Inserting packages in a single transaction does not actually buy us anything as we often delete quads during an insertion and thus, Cayley could not use COPY and do a single round-trip. Inserting multiple packages in a single transaction actually creates deadlocks when a transaction tries to insert (A,B) and another one tries to insert (B,A).
