Update prepare() method on Action subclasses.

Fixes handle()-related strict warnings such as "Strict Standards:
Declaration of AdminPanelAction::prepare() should be compatible with
Action::prepare(array $args = Array)

Ref. #190

plugins/Mapstraction/actions/usermap.php

@@ -44,7 +44,7 @@ if (!defined('STATUSNET')) {
  */
 class UsermapAction extends MapAction
 {
-    function prepare($args)
+    function prepare(array $args = array())
     {
         if(parent::prepare($args)) {
             $this->notice = empty($this->tag)