get jshint error codes

Summary:
makes jshint slightly more useful by printing out error numbers. I love memorizing numbers.
Sorry about the crappy getLintMessageName(). There was no list of error names, just the long descriptions that are already rendered as 'reason'.

Test Plan: Verify that the numbers are mezmorizing. Been tested on OSX with jshint v2.1.11

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D7213