Copyright (c) 2012 Kevin Wellwood
All rights reserved.
This source code is distributed under the Modified BSD License. For terms and
conditions, see license.txt.
Returns True on the first call after the user attempts to close the
application window. In Windows, this is when the user clicks the close
button on the window or presses Alt+F4. In OS X, this is when the user
clicks the red close button on the window, presses Apple+Q, or selects
Quit from the application's menu bar.