Developer credits
Git commits in Moodle 2.3.x by Mike Churchward
commit 54f03faba2543502c82d5a8aa1a248d391f1869d Author: Mike Churchward <mike@remote-learner.net> Date: Wed, 17 Apr 2013 22:18:55 +0800 Tag: v2.3.7 MDL-34933 core_message: Adding index to improve database access on message_working table.