Git commits in Moodle 3.1.5 by Mike Churchward

commit b5c0146072e13aeb384dffc8729f9ecbaadfbcc7
Author: Mike Churchward <mike@remote-learner.net>
Date:   Tue, 15 Nov 2016 05:04:10 +0800
Tag:    v3.1.5

MDL-36233 mod_assign: fixed submission time comparison sql and test.