Git commits in Moodle 3.1.6 by Eric Merrill

commit db370772bd264d022c7c42751f2e4f3151380c8d
Author: Eric Merrill <merrill@oakland.edu>
Date:   Fri, 14 Apr 2017 00:21:13 +0800
Tag:    v3.1.6

MDL-58593 database: More efficiently track issued key names