Id Generation for db4o

Tuna Toksoz just implemented an explicit POID facility for db4o (that doesn't rely on db4o's internal object id system or universal unique ids (UUIDs) used with the db4o Replication System (dRS)). Tuna managed to use the db4o callback facility as an extensibility point to hook this new external ID system so no change to db4o's core source code was necessary. The inspiration came from NHibernate POID Generators and the HiLo algorithm.