Author: Tim Hunt
MDL-29474 prevent install/upgrade if plugin dependancies not met.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=faadd32696237e93500bfec7feadabfd90517058
http://github.com/moodle/moodle/commit/faadd32696237e93500bfec7feadabfd90517058
+ 2.2 en [pluginschecktodo,core_admin]