Fixed typo in import statement of tutorial

Fix authtoken response

Renderer negotiation: media_type specificty evaluation weak

Merge branch 'custom-serializer-form-class' of https://github.com/ludwigkraatz/django-rest-framework into mergebranch#390

Conflicts:
	rest_framework/fields.py
	rest_framework/renderers.py
Manually solved

Update django-filter to released version.

Merge branch 'patch-2' of https://github.com/asfaltboy/django-rest-framework into fix_authtoken_response

Fix location of obtain_auth_token view

api-guide/views.md - add imports to code example

Tutorial: fix module name in section 3

Tutorial: fix module name in section 2

Again snippet -> snippets, but then it could be simpler (and possibly intended) to rename snippets to snippet in the first section of the tutorial.

snippet -> snippets (to match section 1).

* It wasn't clear where `Response` should be imported from.

The `DefaultContentNegotiation` handler uses

For example: Google Chrome sends an Accept-header of `Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8`, when I request a *.png URL.
After matching the media-types with the available renderers (in my case only a custom `PNGRenderer` with a `media_type='image/png'`), only `*/*;q=0.8` is left, which happens to have the same length as the "image/png" media-type defined by the renderer (9 characters).

The specificity of the renderer's media-type over the Accept-header's one is only determined by length.
Using your `_MediaType.precedence` would be preferable in my eyes.

Regards, Fabian

Cache all fields per serializer instance

Add widgets for DateField and DateTimeField

Add support for partial serializer updates