isReadOnly() now takes arguments

Add an array of arguments to isReadOnly() method of actions, to let
them change their results depending on what actions are called.
Primarily used by the 'api' action. Ideally in the future that will be
multiple actions. But this might still be useful.

lib/error.php

@@ -93,7 +93,7 @@ class ErrorAction extends Action
         return $this->message;
     }
 
-    function isReadOnly()
+    function isReadOnly($args)
     {
         return true;
     }