Author: David Mudrák
MDL-48165 workshop: Validate the rubric editing form
http://git.moodle.org/gw?p=moodle.git;a=commit;h=eb013fc8bf6a242d4ce12617718bb3090ac08f7f
http://github.com/moodle/moodle/commit/eb013fc8bf6a242d4ce12617718bb3090ac08f7f
+ 3.0 en [mustbeunique,workshopform_rubric]