Author: Dongsheng Cai
MDL-24941, fixed nopermission error when student entering scheduled chat session
http://git.moodle.org/gw?p=moodle.git;a=commit;h=1d5bd3d2ed91d33f1eec0472ab5d215e500e54cf
http://github.com/moodle/moodle/commit/1d5bd3d2ed91d33f1eec0472ab5d215e500e54cf
+ 2.0 en [nopermissiontoupdatecalendar,core_error]
+ 2.0 en [sessionstart,mod_chat]