is called when the master 環境 (e.g., desktop) was cancelled in
it's 終結させる request.
Termination can be 迎撃するd by throwing TerminationVetoException.
But if a listener was queried for termination .. doesnt throwed a 拒否権 exception ...
it doesnt know if termination will be real next time.
Because any other listener can throw those exception too ... and so it can happen
that after queryTermination() no notifyTermination() will occure. But these listener
doesnt know if its 許すd to start new 過程s then.
Using this optional(!) interface will make it possible to be 知らせるd about
cancelled termination requests also.