Git merges in Moodle 3.1.13 by David Monllao

commit c44b6e79fa988c83567a7f8c89f24f09794eaa2a
Author: David Monllao <davidm@moodle.com>
Date:   Tue, 22 May 2018 15:24:23 +0800
Tag:    v3.1.13

Merge branch 'm31_MDL-61893_Accept_Any_Node_Carbon_Version-minimal' of https://github.com/scara/moodle into MOODLE_31_STABLE