Git commits in Moodle 3.1.1 by Clement Smith

commit 599293befd1b4d5e28f364dc40e51c158a39b6ca
Author: Clement Smith <cdsmith@umn.edu>
Date:   Wed, 01 Jun 2016 02:56:08 +0800
Tag:    v3.1.1

MDL-50824 message/externallib.php: Fix get_string call