Git commits in Moodle 3.1.3 by Brendan Anderson

commit e50b26fa7ca1c7f0a6c52c6970c9c4f862003ded
Author: Brendan Anderson <brendan_anderson@hcpss.org>
Date:   Tue, 25 Oct 2016 03:22:13 +0800
Tag:    v3.1.3

MDL-54112 mod_assign: Add scale null grade filter