Author: Jean-Michel Vedrine
MDL-63905 qtype_multianswer: validate imported questions
http://git.moodle.org/gw?p=moodle.git;a=commit;h=5f9d6e34a3fa4c39b1236be1fdbfebfc1be92581
http://github.com/moodle/moodle/commit/5f9d6e34a3fa4c39b1236be1fdbfebfc1be92581
+ 3.6 en [invalidmultianswerquestion,qtype_multianswer]