* Add some context to exceptions on unserializable
values (addresses #89).
* Document need to format merge data
(into something JSON-serializable).
* Add RemovedInDjrill2 DeprecationWarning.
* Deprecate blanket date/datetime serialization.
(Improves testing accuracy around API response encoding.)
* Add `six` as test dependency (six.BytesIO, six.b)
* Change MockResponse content to bytes (because HTTP responses
are bytes, not strings)
Second attempt to address possible test sequencing issue around tests that alter settings. (Failures in Travis tests not reproducible locally.)
Back-ports override_settings from Django 1.4 for compatibility with Django 1.3.
Add DjrillBackendMockAPITestCase.assert_mandrill_called; use it in representative backend test cases.
(Also make get_api_call_data work with various ways of calling requests.post.)
