Author: Davo Smith
MDL-48074 enrol: option to filter by users 'not in any group'
http://git.moodle.org/gw?p=moodle.git;a=commit;h=0c9d8172b56113763a337b17d6df7ff789c4cffa
http://github.com/moodle/moodle/commit/0c9d8172b56113763a337b17d6df7ff789c4cffa
+ 3.0 en [nogroup,core_enrol]