Stop leaking unittest2 as 'unittest' from django.test.simple

[Jannis Leidel]

This is especially dangerous for cases of from django.test.simple import * where a import unittest comes before.

[Russell Keith-Magee]

(In [14258]) Fixed #14487 -- Prevented unittest from leaking into scope via a 'from django.test.testcases import *' import. Thanks to Jannis for the report.

[Russell Keith-Magee]

Although this bug technically exists in 1.2 as well, I'm not going to backport, The issue isn't as critical with 1.2 because there isn't a second unittest causing problems; plus, this could break code in production. That code probably *should* break, since it's relying on imports that it shouldn't, but it's a breakage that we don't need to enforce.

[Jacob]

Milestone 1.3 deleted