Author: Mark Nelson
MDL-51312 core: added message_deleted event
http://git.moodle.org/gw?p=moodle.git;a=commit;h=b5e617e245345b7556345e523f98816e8d8e098a
http://github.com/moodle/moodle/commit/b5e617e245345b7556345e523f98816e8d8e098a
+ 3.0 en [eventmessagedeleted,core_message]