Author: James Pratt
MDL-41754 (2) quiz statistics : using Sam's new progress classes
http://git.moodle.org/gw?p=moodle.git;a=commit;h=8da6fc9d57d1046dc196959051b949c9c3ed8c79
http://github.com/moodle/moodle/commit/8da6fc9d57d1046dc196959051b949c9c3ed8c79
+ 2.7 en [calculatingallstats,quiz_statistics]