mozilla-services/circus — pull request #595 by schlamar (2013-10-24 06:51:11+00:00)
Title: Do not install unittest2 on Python 2.7.

You don't need unittest2 on 2.7. So the the default test-requirements.txt should be used on 2.7 and 3.3 while only 2.6 installs unittest2.