Author: Mark Nelson
MDL-40913 core_message: replaced 'unblock contact' add_to_log call with an event
http://git.moodle.org/gw?p=moodle.git;a=commit;h=cd60936523a0ddb7c926f4073f2f8188bb018fd2
http://github.com/moodle/moodle/commit/cd60936523a0ddb7c926f4073f2f8188bb018fd2
+ 2.7 en [eventmessagecontactunblocked,core_message]