Git commits in Moodle 3.1.2 by Henning Bostelmann

commit 9a6f6ee022c4d254653c46ee9b47a218d9d7c05f
Author: Henning Bostelmann <henning.bostelmann@york.ac.uk>
Date:   Fri, 19 Aug 2016 00:01:12 +0800
Tag:    v3.1.2

MDL-55627 filter_mathjaxloader: use correct string concatenation op