Author: Issam Taboubi
MDL-52485 tool_lp: Validate the duedate of a plan
http://git.moodle.org/gw?p=moodle.git;a=commit;h=3c5811644c21a0502f5267b1a043205cd21548ca
http://github.com/moodle/moodle/commit/3c5811644c21a0502f5267b1a043205cd21548ca
+ 3.1 en [errorcannotsetduedatetoosoon,tool_lp]