Fix display-buffer interactive spec, and fixes for pop-to-buffer*.

Fix display-buffer interactive spec, and fixes for pop-to-buffer*.

* lisp/window.el (display-buffer): Restore interactive spec.
(display-buffer-same-window, display-buffer-other-window): New
functions.
(pop-to-buffer-1): New function.  Use the above.
(pop-to-buffer, pop-to-buffer-same-window): Use it.
(pop-to-buffer-other-window, pop-to-buffer-other-frame): Deleted.

* lisp/view.el (view-buffer-other-window, view-buffer-other-frame):
Just use pop-to-buffer.