Author: Ryan Wyllie
MDL-64099 message: fix last message and date in group conversations
http://git.moodle.org/gw?p=moodle.git;a=commit;h=12d238100da56a0722d89ae7fa1e8cb8a0818314
http://github.com/moodle/moodle/commit/12d238100da56a0722d89ae7fa1e8cb8a0818314
+ 3.6 en [conversationlastmessage,core_message]
+ 3.6 en [yousender,core_message]