CallWindowProc( wndprcPrev, hwnd, uMsg, wParam, lParam ) -> <lResult>
------------------------------------------------------------------------------


 PARAMETER:

   <nWndprcPrev>   Adress of the previous windows procedure,
                   which is stored in oWnd:OldProc

   <hwnd>          handle of the window that receives the message
   <nMsg>          specifies the message that shall be send
   <nParam>         nfirst message parameter 
   <nlParam>       second message parameter


 DESCRIPTION:

  The CallWindowProc function passes message information to the specified 
  window procedure, and is used for window subclassing. 

  Normally, all windows with the same class share the same window procedure,
  which in our case is the ::HandleEvent Method of the window.
  Fivewin automatically subclasses each new window, so that all messages  
  are intercepted and processed by this method. 

  Any messages not processed by ::HandleEvent must be passed to the 
  previous window procedure by calling CallWindowProc. This allows you 
  to create a chain of window procedures.

 RETURNS:

  The return value specifies the result of the message processing and
  depends on the message sent.