better handling for unicode, should fix some tests

[abdulhaq-e]

The key for all of this is the two functions in test.utils .

I also disabled the test_multiple_id_mixin. I have an almost complete solution for filtering which is compliant with the specifications.

[abdulhaq-e]

So now the failing tests are for drf24 and drf30. Supporting the former is more challenging. However, in my opinion, before attempting to fix those, there needs to be some refactoring. Similar code is repeated in many places and there are some major cases which the renderer can't yet handle. For example, non-paginated lists doesn't work. I fixed it but it needs to be tasted. Supporting drf{24,30} will be much easier then.