Git commits in Moodle 3.1.8 by Adrian Greeve

commit b77e45119c60894f4528e621138055e8304faa81
Author: Adrian Greeve <adrian@moodle.com>
Date:   Thu, 20 Jul 2017 09:52:32 +0800
Tag:    v3.1.8

MDL-57649 mod_lesson: Improvement to upgrade query.

commit 9e1375fac0bd18e7e9e26076933c01fb5ffcd89d
Author: Adrian Greeve <adrian@moodle.com>
Date:   Wed, 19 Jul 2017 15:44:42 +0800
Tag:    v3.1.8

MDL-57649 mod_lesson: Additional refinement to upgrade script.

commit 734fb0f01547e590ebe270bd47334f71d4c9267d
Author: Adrian Greeve <adrian@moodle.com>
Date:   Thu, 13 Jul 2017 12:30:35 +0800
Tag:    v3.1.8

MDL-57649 mod_lesson: Delete answer files correctly.