While we're addressing virtualenv foo, let's ensure we are running
the latest version. This also pulls in newer versions of pip (8.1.1),
setuptools (20.3), and wheel (0.29.0).
MozReview-Commit-ID: G5uSy66Kd6u
--HG--
extra : rebase_source : 804f230adcf77335c79a93537d9623ac3836d9bf
Gregory Szorc