This is an event signal, fired when the window manager requests that
a widget be deleted. This is generally when a user clicks the
X close button on a toplevel window.
The delete event is not propagated. If you want to prevent the
end user from using the window decorations to close your application,
returning true from the
"delete-event" signal will do
just that. Allowing it to return false - which it
does by default - will cause its default handler to be called. This
happens to be the destroy()
method, which in turns fires the
"destroy" signal. In most
cases, it's simpler to connect directly to the latter.
