bug#23621: 25.1.50; Buffer in >1 window; winner-undo recover window point

[Tino Calancha]

For users editing same buffer in differente windows
it may be useful if `winner-undo' could restaure
also the window point from each window.

;; visit same file in 2 windows
./emacs -Q -mm -eval '(progn
                        (find-file-read-only "../src/window.c")
                        (winner-mode 1)
                        (goto-char 1000)
                        (split-window-right)
                        (other-window 1)
                        (goto-char 30500))'

M-! ls ~ RET ; C-x 0 ;; C-x 1 ;;; C-x b
C-c <left>

;; `window-point' return 30500 value for both windows.


;; You may want to preserve > 2 buffr positions.
;; Following example visits different positions of the same
;; buffer in 4 windows.
./emacs -Q -mm -eval '(progn
                        (find-file-read-only "../src/window.c")
                        (winner-mode 1)
                        (goto-char 1000)
                        (split-window-right)
                        (windmove-right 1)
                        (goto-char 30500)

                        (split-window-below)
                        (windmove-down 1)
                        (goto-char 50000)

                        (windmove-left 1)
                        (split-window-below)
                        (windmove-down 1)
                        (goto-char 250000))'

;; As before `window-point' is not preserved for all windows.


In GNU Emacs 25.1.50.3 (x86_64-pc-linux-gnu, GTK+ Version 2.24.30)
 of 2016-05-26 built on calancha-pc
Repository revision: 16be3e90545972dec16014253a843229d5bdf388