unit test for inflight model.refresh call

pertains to #12
1.0.38
tests for out-of-order responses to Model.refresh

pertains to #14
unit tests for Model.save with inflight requests

pertains to #15
added unit test for model.destroy w/ inflight req

pertains to #16
unit test for returning dfd of successful destroy

pertains to #17
added unit test for model.destroy(), model.save()

pertains to #18
sanity check unit test for model.destroy()

pertains to #17
1.0.39