Author: Ryan Wyllie
MDL-64820 forum: add caching to forum_tp_is_tracked
http://git.moodle.org/gw?p=moodle.git;a=commit;h=4dc671a920c08f5d157e6f2336badd4342cd97ad
http://github.com/moodle/moodle/commit/4dc671a920c08f5d157e6f2336badd4342cd97ad
+ 3.7 en [cachedef_forum_is_tracked,mod_forum]