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=df0c2e957899654d744d7f41f5fea6b19c954c09
http://github.com/moodle/moodle/commit/df0c2e957899654d744d7f41f5fea6b19c954c09
+ 2.8 en [manualgradeinvalidformat,core_question]