Git commits in Moodle 3.5.7 by Dan Marsden

commit 8c678d9aa9b862cabb7339f07d3a933955aa0cd4
Author: Dan Marsden <dan@danmarsden.com>
Date:   Fri, 14 Jun 2019 10:02:13 +0800
Tag:    v3.5.7

MDL-60347 core: debugsmtp should be a developer only setting.