Author: Tim Hunt
MDL-63260 qtype_random: orphaned random questions should be deleted
This fix is based on some original code written by Bo Pierce.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=2a0ee3647fc184eb4246554352283223e15cc572
http://github.com/moodle/moodle/commit/2a0ee3647fc184eb4246554352283223e15cc572
+ 3.5 en [taskunusedrandomscleanup,qtype_random]