Author: Henning Bostelmann
MDL-30031 Adaptive question behaviour: ignore invalid answers without penalty
http://git.moodle.org/gw?p=moodle.git;a=commit;h=6a9b5984bdf479f85bacfb13c79554b79438286b
http://github.com/moodle/moodle/commit/6a9b5984bdf479f85bacfb13c79554b79438286b
+ 2.1 en [disregardedwithoutpenalty,qbehaviour_adaptive]