Author: Zachary Durber
MDL-23273 mod_choice: Using locks to ensure choice limits
http://git.moodle.org/gw?p=moodle.git;a=commit;h=a455f2fa45aa7ec2e8a7f52b02972223fb6479bb
http://github.com/moodle/moodle/commit/a455f2fa45aa7ec2e8a7f52b02972223fb6479bb
+ 2.8 en [cannotsubmit,mod_choice]