Author: Jake Dallimore
MDL-63724 core_message: add new group_message_sent event
http://git.moodle.org/gw?p=moodle.git;a=commit;h=aa083ab95f53c3d3a9b9e1f992f095d719903231
http://github.com/moodle/moodle/commit/aa083ab95f53c3d3a9b9e1f992f095d719903231
+ 3.6 en [eventgroupmessagesent,core_message]