MDL-90 authenticate_user_login() - don't accidentally return a bogus $user
MDL-90 authenticate_user_login() - don't accidentally return a bogus $user

While I don't quite understand why we need that $user->id=0, at
_least_ make double sure we don't return it! Callers assume
that if we return an object===success and a user acct that just does
not exist will return an dummy object.

dilawar/moodle