anchor.diff:  
   (defmethod pane-viewport ((pane basic-pane))
     (let ((parent (sheet-parent pane)))
  -    (if (and parent (typep parent 'viewport-pane))
  -	parent
  -      nil)))
  +    (when (and parent (typep parent 'viewport-pane))
  +	parent)))
   
   ;;; Default for streams that aren't even panes.
   
  
positive.code: ;;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  ;;; Boston, MA  02111-1307  USA.
  
  ;;; $Id: panes.lisp,v 1.154 2005/08/19 02:20:35 rstrandh Exp $
  
  (in-package :clim-internals)
  
  
negative.code: 
  (defmethod pane-scroller ((pane basic-pane))
    (let ((viewport (pane-viewport pane)))
      (when viewport
  	(sheet-parent viewport))))
  
  (defmethod scroll-extent ((pane basic-pane) x y)
  