As mentionned to Kenneth on twitter, I originally considered adding this to Django itself but I think this works nicer as a third party app.
All tests seem to pass on my machine, except those involving Python 2.6 because I don't have it installed.
Support for Django 1.4 is a bit tricky because the request attribute is only set on the view during View.dispatch() which means it's not available very early.
I "solved" it with a big warning box in the documentation and skipping a test that was checking just for that.
Added a MessageMixin.
I really like the way this works. 👍