version 13/130803 by Jon Ingold
Section - Closing window chains
[ so set deletion flags for children too, then call delete window safely routine ]
To shut down (g - a g-window):
carry out the window-shutting activity with g.
Window-shutting something is an activity.
For window-shutting a g-window (called g):
if g is g-present and g is not the main-window:
now g is g-unrequired;
now every g-window descended from g is g-unrequired;