override_feature_check and override_feature_checks are two handy

methods that allow enabling or disabling features for unit testing.

Until now, they've been implemented solely as context managers. This

meant adding an additional layer of indentation for tests that needed to

wrap everything inside of them.
This change rewrites these two as classes which inherit from

django.test.utils.TestContextDecorator. This allows these to be used

either as a context manager or as a decorator.

Ran unit tests.
Used these in decorator form elsewhere.