Author: Nelson Moller
MDL-51090: mod_quiz grading validation of an essay question
An invalid format is casted to 0 (if a string) or to some truncated value in other cases (ex: 10..5).
http://git.moodle.org/gw?p=moodle.git;a=commit;h=52b08f5fce1d5980a718219584d5bcd810625ee3
http://github.com/moodle/moodle/commit/52b08f5fce1d5980a718219584d5bcd810625ee3
+ 3.0 en [manualgradeinvalidformat,core_question]