       SippAbortRender
              Set a flag that will cause the current rendering to
              terminate.  This is only useful when called  during
              an  event  update  while rendering in Tk.  If it is
              called while a rendering is not in process, nothing
              is  done.   This  is  designed  for implementing an
              abort button in a Tk application, it  can  also  be
              used in a signal handler.
