Author: Dan Marsden
MDL-28410 Choice - allow single answer choice to be created
http://git.moodle.org/gw?p=moodle.git;a=commit;h=97247fdaddbd11b0599c6bcf64e5894016a7f6c7
http://github.com/moodle/moodle/commit/97247fdaddbd11b0599c6bcf64e5894016a7f6c7
+ 2.1 en [atleastoneoption,mod_choice]