Code review comment for lp:~bac/launchpad/bug-496701-mimetypes

I see that this change is to the python env, not Launchpad, because it is the only guaranteed location to support our desire for a single mimetypes that just works. This is good to land since we do need this.

We can reconsider this if we get site.py work as we expect, or Python 2.6 works as we require.