Ticket 23600

Make django.core.files.storage.default_storage take account of overriding of the following settings:

MEDIA_URL
FILE_UPLOAD_PERMISSIONS
FILE_UPLOAD_DIRECTORY_PERMISSIONS

Sure the imports can go at the top. I can't think why I didn't do that originally.

As far as the location of the tests goes, I can't think of anywhere better - they're with existing tests to do with overriding settings for testing.