#99 Add manual sync/close to Graph

[Andrew Newman]

Now that Graph is properly refactored and BTree is being written out on adds/removes - allow users to call close and sync/refersh (possibly) on graph to ensure that changes are written to disk.

The "close" method on graph currently does nothing.

A similar method should be on the CollectionFactory and MapFactory. Used by the top level factories to ensure data is written to disk.

Both should sync the BDB environment value - as these are not written out yet (apparently). The BTree is now written out.

[Andrew Newman]

Actual implementation is discussed here:
http://code.google.com/p/jrdf/wiki/PersistentGraphs

Basically factories do not monitor resources - graph close() must be called.