Author: Dongsheng Cai
MDL-25069 CHAT added event handler to handler user logout event.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=a8e3b008ff40b332227b5fe2d87422aaa9760dc1
http://github.com/moodle/moodle/commit/a8e3b008ff40b332227b5fe2d87422aaa9760dc1
+ 2.0 en [notlogged,mod_chat]