Git commits in Moodle 2.9.4 by Dmitrii Metelkin

commit 8aa81abdc0e77663e847ab4c4b9c1703014c86d3
Author: Dmitrii Metelkin <dmitriim@catalyst-au.net>
Date:   Fri, 06 Nov 2015 12:23:38 +0800
Tag:    v2.9.4

MDL-51314 mod_assign: cache group membership in can_edit_submission