document conflict resolution. bugfix the situation in which comparing persistent objects (for instance, as members in BTree set or keys of BTree) might cause data inconsistency during conflict resolution.  support multidatabase references in conflict resolution.  make it possible to examine oid and (in some situations) database name of persistent object references so that I can add some code to zope.app.keyreference to support these objects (so BTree conflict resolution can happen at all when keyreferences are used).  I will add information to CHANGES after Jim reviews (or sooner).