More window code related fixes and documentation changes.

More window code related fixes and documentation changes.

* window.c (Fother_window_for_scrolling): Check that
Vother_window_scroll_buffer is a buffer.
* window.el (fit-frame-to-buffer, fit-frame-to-buffer-margins):
Fix doc-strings.
(fit-frame-to-buffer): New argument ONLY.  Remove dependency on
fit-frame-to-buffer variable.  Fix doc-string.
(fit-window-to-buffer): Set ONLY argument in call of
fit-frame-to-buffer.  Fix doc-string.
* frames.texi (Size and Position): Rewrite entries for
`fit-frame-to-buffer' and `fit-frame-to-buffer-margins'.  Add
description for `fit-frame-to-buffer-sizes'.
* windows.texi (Resizing Windows): Add descriptions for
pixelwise resizing.  Add entries for `window-resize-pixelwise'
and `fit-window-to-buffer-horizontally'.  Rewrite
`fit-window-to-buffer' entry.