R1:9891394e80d6

Phabricator now checks whether pygmentize script can be run when user enables pygments

Summary: Check if pygmentize is runnable if pygments is enabled

Test Plan: Enable pygments with pygmentize unavailable in path

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5157