This patch makes it possible to use the NT GUI with a Cygwin core Emacs.
 The patch is still a little rough around the edges, but it works well
enough to let me do real work in this new Emacs configuration.  For me,
at least, forgoing the hassle of an X server and gaining some
integration makes the new configuration worthwhile.

(Of course, I don't plan to merge this before the feature freeze ends.
Do we have an emacs-next branch of some sort?)

What works:

  - All the usual Cygwin features, including multitty, real ptys, job
control, etc.

  - Native NT GUI

  - File dialogs

What's new:

  - Rewritten clipboard system mostly implemented in lisp

  - Preserving formatting when copying text into other applications
(probably better structured as a separate package using the extensible
clipboard system)

What doesn't work yet:

  - The normal NT build (I don't have a toolchain to test it)

  - Graphical menus in customize

What I haven't tested:

  - Image support