Git commits in Moodle 3.4.0 by Adam Olley

commit d12ac535125eab9fc2ff643c778b60b526b2e53a
Author: Adam Olley <adam.olley@blackboard.com>
Date:   Tue, 03 Oct 2017 07:46:18 +0800
Tag:    v3.4.0-beta

MDL-60320 icons: Use PNG icons as the preview thumbnails

commit 556ceb207145ce5e798696831d787af67350553b
Author: Adam Olley <adam.olley@blackboard.com>
Date:   Thu, 20 Apr 2017 10:11:59 +0800
Tag:    v3.4.0-beta

MDL-58651 logstore_database: Add ability to not send database options