Merge pull request #288 from bdeggleston/master

misc rexpro fixes part 2
Update CHANGELOG.textile
Fix bug in close on RexsterClient.

Check for a null connection before closing as a connection may not have been initialized or may have been nulled in the event of an exception.
Merge remote-tracking branch 'origin/master'
Serialize map keys in RexPro properly.

Map keys must be either string or number.  Everything else is converted via toString.  Not sure there is a better way.
Stub in explicit tree serialization in rexpro.
changing rexpro {element:val} map types serialization to {element_id: {'_element': element, '_contents': val}}