Author: Henning Bostelmann
MDL-30031 Adaptive question behaviour: ignore invalid answers without penalty
http://git.moodle.org/gw?p=moodle.git;a=commit;h=096c30165b18ebd4f4c5c03f3d2aa31ca161450a
http://github.com/moodle/moodle/commit/096c30165b18ebd4f4c5c03f3d2aa31ca161450a
+ 2.3 en [disregardedwithoutpenalty,qbehaviour_adaptive]