Git commits in Moodle 3.4.5 by Zig Tan

commit 3b7ead71a48ad67cfd97856100fba64bf04f5ad8
Author: Zig Tan <zig@moodle.com>
Date:   Fri, 29 Jun 2018 17:07:35 +0800
Tag:    v3.4.5

MDL-61870 mod_assign: Fix/clean up imported group override duedates


commit ae25d0ec2ceb3791df4ade94f7f750715432fcb7
Author: Zig Tan <zig@moodle.com>
Date:   Fri, 29 Jun 2018 11:21:45 +0800
Tag:    v3.4.5

MDL-61870 mod_assign: Fix/clean up imported group override duedates


commit 79c0b489dd9bc6bcc85307d7b2b365b7463d83f2
Author: Zig Tan <zig@moodle.com>
Date:   Mon, 18 Jun 2018 16:41:53 +0800
Tag:    v3.4.5

MDL-38301 mod_assign: Fix date validation logic & message consistency