Added method for retrieving objects from a bucket with a predicate filter
Tweaked credential storage and made unit tests use new keychain and app ID
Revert to using username in keychain, plus better sign out handling
Send the names of member names that changed to bucket delegate's didChangeObjectForKey method
Properly check for revised optional delegate method
Updated unit tests to use new delegate method
Removed hardcoded 'config' simperiumKeys from unit tests
Merge pull request for ARC
Support specifying custom NSValueTransformer names for Core Data transformable attributes