Author: Damyon Wiese
MDL-58220 oauth2: obey $CFG->authpreventaccountcreation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=6cee96c8afa756f1fb37dda0cd9a0e527b6eb1a6
http://github.com/moodle/moodle/commit/6cee96c8afa756f1fb37dda0cd9a0e527b6eb1a6
+ 3.3 en [loginerror_cannotcreateaccounts,auth_oauth2]