Author: Ashley Holman
MDL-34989 assign: Allow students to submit when grade is overriden
Also inform teachers when grading is disabled due to gradebook lock/override.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c33b4c81bb76b8719ad4bd14eca8263c2d6805ec
http://github.com/moodle/moodle/commit/c33b4c81bb76b8719ad4bd14eca8263c2d6805ec
+ 2.6 en [gradelocked,mod_assign]