lint fixes

Summary:
I'm not quite sure why I linted this file, but I think
I'm going to start leaving files I touch in the analytics repo
linted. Which I guess should be audits. But you can let me know
if you think this is a bad/annoying idea.

Test Plan: lint!

Reviewers: jace

Differential Revision: http://phabricator.khanacademy.org/D4121
make multithreading work on linux
improve versatility of roc curve generator