Author: Julien Boulen
MDL-45743 forum: trigger an event when changing subscription mode
http://git.moodle.org/gw?p=moodle.git;a=commit;h=8d36ef8dbc8ee511fe363dd25ba951e8157b41e3
http://github.com/moodle/moodle/commit/8d36ef8dbc8ee511fe363dd25ba951e8157b41e3
+ 4.3 en [eventforumsubscriptionupdated,mod_forum]