Duplicating Managed Objects

The bug found due to [this StackOverflow post][1] fixed the mapping issue, however it seems that it's duplicating managed objects in the array. This pull copy-pastes the previous unit test, with the addition of pre-populating the MOC with objects.

*Sorry, but I couldn't get the tests to build and run, and so I'm not certain they are valid. They should be expressive enough to get the ball rolling*

[1]: http://stackoverflow.com/questions/14532961/restkit-relationship-mapping