Allow scrolling in y-or-n-p.

Allow scrolling in y-or-n-p.

* lisp/replace.el (query-replace-map): Bind four new symbols for
requesting window scrolling.

* lisp/subr.el (y-or-n-p): Handle the window-scrolling bindings in
query-replace-map.

* lisp/custom.el (custom-theme-load-confirm): Use y-or-n-p.

* lisp/window.el (scroll-other-window-down): Make the arg optional.

* lisp/emacs-lisp/map-ynp.el (map-y-or-n-p): Don't bind scrolling keys
since they are now in query-replace-map.

* doc/lispref/minibuf.texi (Yes-or-No Queries): Document recentering and
scrolling in y-or-n-p.  Remove gratuitous example.

* doc/lispref/searching.texi (Search and Replace): Document window scrolling
entries in query-replace-map.