Developer credits
Git commits in Moodle 2.4.x by Mike Churchward
commit d75a987e36e68f9c3000fb93e85ea42dd5fa38a2 Author: Mike Churchward <mike@remote-learner.net> Date: Wed, 17 Apr 2013 22:31:46 +0800 Tag: v2.4.4 MDL-34933 core_message: Adding index to improve database access on message_working table.