Git commits in Moodle 2.9.7 by Kevin Wiliarty

commit e647d73811d36c37020d7220b48119616377cb74
Author: Kevin Wiliarty <kevin.wiliarty@gmail.com>
Date:   Wed, 27 Apr 2016 01:18:43 +0800
Tag:    v2.9.7

MDL-54620 ratings: display '0' when aggregate = 0