Git commits in Moodle 3.6.4 by Leon Stringer

commit 435d91e4bbd0b595f35aed2a27c712c3d708984c
Author: Leon Stringer <leon@priorsvle.com>
Date:   Sat, 30 Mar 2019 00:09:33 +0800
Tag:    v3.6.4

MDL-64719 cache: Implement purge_current_user() in \cache