Git commits in Moodle 3.6.4 by Mark Nelson

commit a3d19efab4aff83c07db9f0ad34c8f0e1f29c64c
Author: Mark Nelson <markn@moodle.com>
Date:   Tue, 16 Apr 2019 18:40:16 +0800
Tag:    v3.6.4

MDL-65365 core_message: prevent users from viewing all conversations


commit 22f75de983a262aebc13d6411b6fc6ff1f7840d0
Author: Mark Nelson <markn@moodle.com>
Date:   Mon, 25 Mar 2019 17:12:53 +0800
Tag:    v3.6.4

MDL-65173 message_email: removed bogus logic


commit 5806a1f2517be9424d0b6427f4a26f11e7e9572f
Author: Mark Nelson <markn@moodle.com>
Date:   Wed, 06 Mar 2019 14:57:05 +0800
Tag:    v3.6.4

MDL-64990 tool_usertours: do not show messaging tour when disabled


commit 93f39f3db62b44da250416a191dde449dd89c805
Author: Mark Nelson <markn@moodle.com>
Date:   Mon, 25 Feb 2019 10:45:28 +0800
Tag:    v3.6.4

MDL-64568 core_group: delete conversation and members on group deletion


commit c47c19634ed39d15065575dfd421faaf75596eba
Author: Mark Nelson <markn@moodle.com>
Date:   Mon, 25 Feb 2019 08:53:59 +0800
Tag:    v3.6.4

MDL-64568 core: upgrade step to remove orphaned group conversations