bug#20848: 24.5; window-state-put fails when strongly dedicated windows are involved

[Vasilij Schneidermann]

> The dedicated status is stored for each live window individually and
> should be restored as such.  Did you try it?

Yes, the patch works for me.  To accomodate for Emacs 24.3, 24.4 and
24.5, I've modified my example to contain a workaround:

(progn
  (switch-to-buffer "*Messages*")
  (let ((old-window-config (window-state-get)))
    (set-window-dedicated-p nil t)
    (switch-to-buffer-other-window "*scratch*")
    (when (version<= emacs-version "24.5")
      (delete-other-windows)
      (set-window-dedicated-p nil nil)
      (window-state-put old-window-config (frame-root-window)))))
 
> The state of the argument window of ‘window-state-put’ is destroyed by
> the latter so I have no idea how that could be done.
 
I thought of introducing a variable roughly equivalent to
`inhibit-read-only' which state is checked by a few window primitives.
If it were bound, functions like `set-window-buffer' wouldn't error out
for dedicated windows at all.