bug#25875: 26.0.50; Hang logging out of MS-Windows

[Richard Copley]

If you want to block or delay a shutdown in recent
Windows versions you need to use
ShutdownBlockReasonCreate (it's unfortunate, but
we lazy programmers proved we couldn't be trusted,
collectively, to handle WM_QUERY_ENDSESSION
correctly, so the arms race had to be escalated in
order to allow users to shut down their computers
reliably).

Ken, what was the original change intended to guard
against? What would people be doing with Emacs that
can't simply be abandoned? Did you have a particular
example in mind?