Author: Julien Boulen
MDL-76314 forum: add form check to prevent combining wrong parameters
Form validation prevents combining the forum type "single discussion" and the group mode "separate groups".
http://git.moodle.org/gw?p=moodle.git;a=commit;h=002ed2d8670a450101e4dbd3f554157c570dbf4f
http://github.com/moodle/moodle/commit/002ed2d8670a450101e4dbd3f554157c570dbf4f
+ 4.0 en [cannotuseseperategroupsandsingletopic,mod_forum]
+ 4.0 en [cannotusesingletopicandseperategroups,mod_forum]