'AbortAutoAccount': Return false to cancel automated local account creation, where normally authentication against an external auth plugin would be creating a local account.
$user: the User object about to be created (read-only, incomplete)
-&$abortMessage: out parameter: error message to be displayed to user
+&$abortMsg: out parameter: name of error message to be displayed to user
'AbortAutoblock': Return false to cancel an autoblock.
$autoblockip: The IP going to be autoblocked.
'AbortNewAccount': Return false to cancel explicit account creation.
$user: the User object about to be created (read-only, incomplete)
-&$message: out parameter: error message to display on abort
+&$msg: out parameter: name of error message to display on abort
'AddNewAccount': after a user account is created
$user: the User object that was created. (Parameter added in 1.7)