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.
Possible issue here... you are storing the objectID's above in the background context, and calling `save` to persist these objects in the `backgroundContext`.  However, then here you query the main `self.context` for these objectIDs... and in my app I'm getting back the previous copy of an object.  (if I have a User object already in the store, and then a response comes back with the same ID but different data payload, it seems to be persisted in the store, but `self.context` has the old copy still, which is what gets returned)

I tried changed the above code to just put the records directly in the NSMutableArray are return it... rather than storing the objectIDs and then re-querying for them... but this didn't work.  (I guess you had a good reason for doing it this way)

Adding this `refreshObject` line did fix my issue however:
```ruby
            NSManagedObject *record = [self.context objectWithID:objectID];
            [self.context refreshObject:record mergeChanges:NO];
            [records addObject:record];
```