Git commits in Moodle 2.5.3 by Jody Steele

commit 94b2dbb9b5e0da5efddf9eb496865d5fb2fe3d89
Author: Jody Steele <steelej@queensu.ca>
Date:   Wed, 16 Oct 2013 23:19:34 +0800
Tag:    v2.5.3

MDL-38628 mod_assign: Allow a user to specify "No Grade" when grading an assignment submission