Git commits in Moodle 3.5.5 by Mark Johnson

commit 4c0a87629f157b8fd7e226badd7635bc387cd60f
Author: Mark Johnson <mark.johnson@open.ac.uk>
Date:   Mon, 18 Feb 2019 22:03:52 +0800
Tag:    v3.5.5

MDL-64889 completion: Fix performance of get_course_progress_percentage