Author: Andrew Davis
MDL-26275 grade: added a safety check to avoid hitting PHP's max_input_var by reducing the number of students per page if necessary
http://git.moodle.org/gw?p=moodle.git;a=commit;h=d3b698a46e8a64e7a536f33e67d57ec11caf268c
http://github.com/moodle/moodle/commit/d3b698a46e8a64e7a536f33e67d57ec11caf268c
+ 2.3 en [studentsperpagereduced,core_grades]