Add original object to bundle

[SeanHayes]

By the time authorization happens, the request data has been hydrated onto the object retrieved from the DB. Sometimes devs need to validate against the original values on the model, and it would be nice not to have to do another query.

See: http://stackoverflow.com/questions/35391634/tastypie-authorization-not-exactly-authorizating

[SeanHayes]

Would help solve #1051