Author: Andrew Nicols
MDL-1626 mod_forum: Add functions to change user discussion subscription state
http://git.moodle.org/gw?p=moodle.git;a=commit;h=e3bbfb52c4b5d951804934f4eacbcb682141fc14
http://github.com/moodle/moodle/commit/e3bbfb52c4b5d951804934f4eacbcb682141fc14
+ 2.8 en [eventdiscussionsubscriptioncreated,mod_forum]
+ 2.8 en [eventdiscussionsubscriptiondeleted,mod_forum]