Stop triggering Django 1.5 DeprecationWarning

As per the [Django deprecation timeline][0], HttpRequest.raw_post_data has been renamed HttpRequest.body.

[0]: https://docs.djangoproject.com/en/1.5/internals/deprecation/#id3
Make tests work again

Updated the test settings to use newer DATABASES style.
Fixed typo in test_positional_args that was causing a test failure.
Restore compatibility with Django 1.2 & 1.3
Merge pull request #44 from davea/fix_django15_warning

Using HttpRequest.raw_post_data triggers DeprecationWarning