Turn on the calling runlint.py when we commit files via git and hg.

Summary:
Depends on D3742, which makes runlint.py fast enough we can run it on
every commit.

Test Plan:
Fingers crossed.  I tested the extra-linter functionality when I added
it, but we'll have to wait until D3742 is in to test it end-to-end
again.

Reviewers: chris

Reviewed By: chris

Differential Revision: http://phabricator.khanacademy.org/D3743