Git commits in Moodle 2.8.9 by Sam Chaffee

commit f0d7264769cb56740094d2d0defc58d900987bd3
Author: Sam Chaffee <sam@moodlerooms.com>
Date:   Sat, 03 Oct 2015 01:28:15 +0800
Tag:    v2.8.9

MDL-51514 gradebook: Optimize set_usedinaggregation query for MySQL