Author: Andrew Nicols
MDL-48029 mod_forum: Check for subscription before enrolling
http://git.moodle.org/gw?p=moodle.git;a=commit;h=ddb4a31d54aece5e75e1af0ffe98ddacbb236530
http://github.com/moodle/moodle/commit/ddb4a31d54aece5e75e1af0ffe98ddacbb236530
+ 2.8 en [noguestsubscribe,mod_forum]