Git commits in Moodle 3.3.x by Jonathan Champ

commit d3a6b91aecfdc371cbb081e6235f1632d9b46430
Author: Jonathan Champ <jonathan_champ@ncsu.edu>
Date:   Sat, 17 Dec 2016 01:20:45 +0800
Tag:    v3.3.0-beta

MDL-57427 cache: Use perfdebug only when enabled