Fix issue with AFMMRecordResponseSerializer threading

I created a new pull request with some additional error handling using the built in debugger. @jonbrooks please take a look.
If I understand your question, you're asking why not just return the array of NSManagedObjects that we get from the backgroundContext?  Ultimately, we want to return NSManagedObjects associated with the main context.  The work here is all done on the backgroundContext (this is now the context associated with the recordResponse), and the returned objects are associated with that context.  We must then use ObjectID as a way of translating those same objects to the main context.  Does that answer your question?