Author: Marina Glancy
MDL-49003 login: prevent signup when user is logged in
http://git.moodle.org/gw?p=moodle.git;a=commit;h=6a2c10a89dd7a6d9e8e65dcb53224358776c2edd
http://github.com/moodle/moodle/commit/6a2c10a89dd7a6d9e8e65dcb53224358776c2edd
+ 2.9 en [cannotsignup,core_error]