Git commits in Moodle 2.9.1 by GeekSmith

commit 7c6d8dd8e0932d2821ffda5ab2f6a184019d76af
Author: GeekSmith <cbmegahan@geeksmith.com>
Date:   Sat, 13 Jun 2015 04:21:50 +0800
Tag:    v2.9.1

MDL-50583 upgrade: Optimize upgrade_minmaxgrade