Don't clone objects in the persistence cache; instead,
ensure that one instance per object is used/given
wherever possible. Goal is to keep object state in
sync between visible instances for WTD-791 et al.
Move cache sources into their own bundle, for reuse with other
persistence adapters; specifically supports the persistence
adapter to the WARP Server, which is non-Couch but which will
want to use this cache. WTD-702.
