Git commits in Moodle 2.8.7 by GeekSmith

commit d932630feb1c62bbb874835208da8bc8f6a59079
Author: GeekSmith <cbmegahan@geeksmith.com>
Date:   Sat, 13 Jun 2015 04:21:50 +0800
Tag:    v2.8.7

MDL-50583 upgrade: Optimize upgrade_minmaxgrade