Fix GET-after-POST redirect in plugin manager

The redirect target URL is constructed with escaped ampersands since b6258081.
Thanks to Chris Tapp for pointing out.

lib/plugins/plugin/classes/ap_manage.class.php

@@ -121,7 +121,7 @@ class ap_manage {
 
         // update latest plugin date - FIXME
         global $ID;
-        send_redirect(wl($ID,array('do'=>'admin','page'=>'plugin'),true));
+        send_redirect(wl($ID,array('do'=>'admin','page'=>'plugin'),true, '&'));
     }
 
     /**