Author: Sam Hemelryk
MDL-36297 caching: added for HTML purified text
http://git.moodle.org/gw?p=moodle.git;a=commit;h=e85c56ccb87f7000f91472e50cb16d4ac0a304a4
http://github.com/moodle/moodle/commit/e85c56ccb87f7000f91472e50cb16d4ac0a304a4
+ 2.5 en [cachedef_htmlpurifier,core_cache]