QueryParameterVersioning does not fall back to the value used in the `DEFAULT_VERSION` setting, while other versioning schemes do. This looks like a minor change, and incorporates the `self.default_version` set in the superclass.

I'll sheepishly admit that I edited this inline without running any tests or anything, so please let me know if this needs more work.

Display py.test internal warnings

Regarding #3729

Document how to tweak authtoken.admin.TokenAdmin

python -Werror generates warnings informing that on_delete is a required keyword in Django 2.0

With focus on large user base, but can be extended.

2015 update in __init__.py file

update copyright 2016

Fixed TimeField not handling empty values

PY2: DateField.to_representation can't work with unicode value

Fixes #3786

Added documentation for the third party jsonapi.org package

Fix nested validation error being rendered incorrectly.

Minor fix for dictionary key lookup in settings file

Fixes #3804, avoiding update of Meta.extra_kwargs

Added unit test to cover.

Typo fix in docs/api-guide/relations.md

`slug field` in code snippet was replaced to `slug_field`

Previously an extra list wrapped nested validation errors raised from serializer's validate() methods.
That was inconsistent with the format of validation errors raised by validate_<fieldname> methods.
i.e. these two resulted in *different* behaviour:

    def validate_foo(self):
        raise ValidationError(['bar'])

    def validate(self):
        raise ValidationError({'foo': ['bar']})

don't import authtoken model until needed

Min/MaxValueValidator is no longer transferred from a model's DecimalField

These two tests were previously added in
https://github.com/tomchristie/django-rest-framework/commit/7d79cf35b7be01b175d8c25276a4414e8144a16b
but we have now discovered that there are not actually two separate
cases, there was just a  bug in the code that made it look that way.

This also removes a redundant check to see if `DecimalValidator` was
defined.

Make code block consistent in serialization tutorial

All the other code blocks in the Serialization tutorial can be copied and pasted, but there is one that includes the >>> shell prompt characters. This commit removes those characters, and also makes the output consistent with other code blocks by making it a comment.

Initial fixes #3636 and fixes #3637

Add HTTP status code 451 to status.py

This test was incorrectly checking that there were no validators set in
older versions of Django, even though it should have been checking for
the two validators that were set up on the model field level.

The originally regression test that this fixes was added in
https://github.com/tomchristie/django-rest-framework/commit/7d79cf35b7be01b175d8c25276a4414e8144a16b
when fixing an issue with the `DecimalValidator`.

Previously, all validators set on a DecimalField in Django would be
stripped when converted to a Django REST framework field. This was
because any validator that was an instance of `DecimalValidator` would
be removed, and when `DecimalValidator` wasn't supported (so it was
`None`), all validators would be removed.

This fixes the issue by only removing the `DecimalValidator` instances
if the `DecimalValidator` is supported.