Git commits in Moodle 2.9.7 by Andrew Nicols

commit 81fcfc206528a42b11ea4948daf1eff649c8259a
Author: Andrew Nicols <andrew@nicols.co.uk>
Date:   Wed, 18 May 2016 12:04:44 +0800
Tag:    v2.9.7

MDL-54620 rating: Add tests for get_aggregate_string