Git commits in Moodle 3.1.9 by Davo Smith

commit c614487d2d823917fbe5f5e54137422056bef202
Author: Davo Smith <davo.smith@synergy-learning.com>
Date:   Fri, 06 Oct 2017 19:46:05 +0800
Tag:    v3.1.9

MDL-60366 mod_feedback: fix deletion of valid anonymous duplicates