Git commits in Moodle 3.4.0 by Fred Woolard

commit bd035b98fdf182d2b517944f6cde3588523dee04
Author: Fred Woolard <woolardfa@appstate.edu>
Date:   Tue, 24 Oct 2017 01:22:42 +0800
Tag:    v3.4.0-beta

MDL-57477 core: If memcached 3.x mimic 2.2.0 lock acquisition behavior