Git commits in Moodle 3.8.x by deraadt

commit b16b681a79d56776e9209a10c9290323548d5f61
Author: deraadt <michaelderaadt@gmail.com>
Date:   Thu, 16 Apr 2020 09:47:45 +0800
Tag:    v3.8.4

MDL-68425 user: Add capability check for messaging