Make "purge_cache.php --differential" also purge the inline comment cache
Summary: We purge the cache for primary comments only right now, not inline
comments.
Test Plan: Ran "purge_cache.php --differential".
Reviewers: btrahan, jungejason
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T683
Differential Revision: https://secure.phabricator.com/D1451