Adding tests for obj_update with identifiers

This test exercises obj_update when grabbing an object using its uri
identifiers.

Currently lines 1915-1934 cover this special case and there is no
test case for them. If you comment out those lines and run the whole
test suite, it will pass.
Sending PUT requests should now be much more efficient,
as ``full_hydrate`` is no longer called twice. Thanks to
maraujop for most of the work!
Vastly improved the ``Vary`` & ``Cache-control`` headers &
hence improved how cacheable GET requests are. Thanks to
ross for the original patch.
Fixed an import error in tests. Thanks to dirn for the report!
Fix a bad cherry-pick and make tests pass again
Remove AdminMediaHandler.

AdminMediaHandler was removed in Django 1.5.
Add dev builds to travis.
Added 'hammock' to 'docs/tools.rst'
Add content types to setup.py, Fixes a bug reported in IRC by berndt
Try/Except for import of constant which was moved for django 1.5

Closes #671
Added a contributing doc for bonus GH integration.
Fixed simple typo in "The Hydrate Cycle" section.
Django dev JSONSerializer is now based on json

Djando dev breaks Tastypie serialization. Tastypie uses Django
`json.JSONEncoder`, which was based on simplejson in previous versions,
but it's now based on json, which doesn't accept a keyword argument
`namedtuple_as_object` anymore.

So in Django 1.5 we need to pass `JSONEncoder` to json, instead of
simplejson
Merge pull request #676 from hroart/patch-1

Fixed simple typo in "The Hydrate Cycle" section.
Fix typo in ``__unicode__`` of ApiAccess model.

Thanks to @exister for the report.
Test GFK in tox.
Fix extra "how"s in docs.

Thanks to @ta5ae for the report.
Make ToOneField respect readonly during save_related
Escape \u2028 and \u2029 in JSONP.

Thanks to @vfaronov for the report.
Don't count Django dev builds as failures in Travis.