Install new buffer display functions and variables.

Install new buffer display functions and variables.

* window.el (display-buffer-function): Rewrite doc-string.
(display-buffer-window, display-buffer-alist): New variables.
(display-buffer-split-specifiers)
(display-buffer-side-specifiers)
(display-buffer-macro-specifiers): New constants.
(display-buffer-even-window-sizes, display-buffer-set-height)
(display-buffer-set-width, display-buffer-select-window)
(display-buffer-in-window, display-buffer-reuse-window)
(display-buffer-split-window-1, display-buffer-split-window)
(display-buffer-split-atom-window, display-buffer-pop-up-window)
(display-buffer-pop-up-frame, display-buffer-pop-up-side-window)
(display-buffer-in-side-window, normalize-buffer-to-display)
(display-buffer-normalize-specifiers-1)
(display-buffer-normalize-specifiers-2)
(display-buffer-normalize-specifiers, display-buffer-frame): New
functions.
(display-buffer): Major rewrite.
(display-buffer-other-window, display-buffer-other-frame)
(pop-to-buffer, switch-to-buffer-other-window)
(switch-to-buffer-other-frame): Rewrite.
(display-buffer-same-window, display-buffer-same-frame)
(display-buffer-same-frame-other-window)
(pop-to-buffer-same-window, pop-to-buffer-same-frame)
(pop-to-buffer-other-window)
(pop-to-buffer-same-frame-other-window)
(pop-to-buffer-other-frame, switch-to-buffer-same-frame)
(switch-to-buffer-other-window-same-frame): New functions.
(same-window-p, special-display-p): Rewrite disabling warnings.
Make obsolete.
(pop-up-frames, display-buffer-reuse-frames, pop-up-windows)
(display-buffer-mark-dedicated): Initialize to symbol 'unset.
Make obsolete
(same-window-buffer-names, same-window-regexps)
(special-display-frame-alist, special-display-popup-frame)
(special-display-function, special-display-buffer-names)
(special-display-regexps, pop-up-frame-alist)
(pop-up-frame-function, split-window-preferred-function)
(split-height-threshold, split-width-threshold)
(even-window-heights): Make obsolete.