MDL-23245 Added support for new style of auth plugin configuration

This hack allows auth plugins to migrate to the new auth_xxx naming
style (as happened with auth_mnet in my previous commit).

admin/auth_config.php

@@ -43,7 +43,9 @@
         }
     }
 } else {
-    $frm = get_config("auth/$auth");
+    $frmlegacystyle = get_config('auth/'.$auth);
+    $frmnewstyle    = get_config('auth_'.$auth);
+    $frm = (object)array_merge((array)$frmlegacystyle, (array)$frmnewstyle);
 }
 
 $user_fields = $authplugin->userfields;