Author: Petr Skoda
MDL-24258 backporting security fix
http://git.moodle.org/gw?p=moodle.git;a=commit;h=939e0afcd57185da2734c857eb1d822135dcb573
http://github.com/moodle/moodle/commit/939e0afcd57185da2734c857eb1d822135dcb573
+ 1.8 en [cannotdeletepost,mod_forum]