NAME
       WM_OPEN -- open a window

   SYNOPSIS
       window = DoMethod( winobj, WM_OPEN );

   FUNCTION
       This function opens the window the object should be handling.
       If the window is already open, it does nothing. If no shared
       message port is set, a message port will be created for this
       window.

   RESULTS
       window -- a pointer to the struct window for this window, or
               NULL if the window could not be opened.