Author: Andrew Nicols
MDL-76867 core_admin: Standardise plugin management when plugin missing from disk
http://git.moodle.org/gw?p=moodle.git;a=commit;h=573066ba5f15e772a383351974363c463b0042d3
http://github.com/moodle/moodle/commit/573066ba5f15e772a383351974363c463b0042d3
+ 4.2 en [pluginmissingfromdisk,core]