Author: Ryan Wyllie
MDL-66770 mod_forum: put nested v2 display mode behind user preference
http://git.moodle.org/gw?p=moodle.git;a=commit;h=667e5fd93f0dea69ea5d24a887083f7d6da781f6
http://github.com/moodle/moodle/commit/667e5fd93f0dea69ea5d24a887083f7d6da781f6
+ 3.8 en [useexperimentalui,mod_forum]