Provide new semantics for variable display-buffer-window (former

Provide new semantics for variable display-buffer-window (former
display-buffer-window-and-buffer) and quit-restore window parameter.

* window.el (window-deletable-p, quit-restore-window): Adapt to
new quit-restore semantics.
(split-window-quit-restore): Remove.
(split-window-vertically, split-window-horizontally):
Unconditionally copy quit-restore parameter to new window.
(display-buffer-names): Mention quit-restore window parameter.
(display-buffer-window-and-buffer): Rename to
display-buffer-window and rewrite doc-string.
(display-buffer-in-window, display-buffer-in-lru-buffer-window)
(display-buffer-in-lru-window, display-buffer-in-new-window)
(display-buffer-in-new-frame, display-buffer): Move quit-restore
parameter handling from display-buffer-in-window to the callers.
Set display-buffer-window.

* help.el (help-window-setup, with-help-window): Use
display-buffer-window insted of display-buffer-window-and-buffer
and adapt to new semantics of the former.

* windows.texi (Buffers and Windows, Displaying Buffers): Adapt
to new semantics of quit-restore window parameter and
display-buffer-window (was display-buffer-window-and-buffer)
semantics.