(whitespace-indent-regexp): Make this match any multiples of eight spaces near

(whitespace-indent-regexp): Make this match any multiples of eight spaces near
the beginning of a line.
(whitespace-buffer): Use `remove-overlays' instead of
`whitespace-unhighlight-the-space' and `overlay-recenter' to speed up overlay
handling.
(whitespace-buffer-leading, whitespace-buffer-trailing): Make these functions
highlight the text removed by `whitespace-buffer-leading-cleanup' and
`whitespace-buffer-trailing-cleanup' respectively.
(whitespace-buffer-search): Use `with-local-quit'.  Move `format' out of loop
to speed up scanning larger buffers.
(whitespace-unhighlight-the-space): Remove `remove-hook' since that function is
never added to a hook.
(whitespace-spacetab-regexp, whitespace-ateol-regexp)
(whitespace-buffer-leading-cleanup)
(whitespace-refresh-rescan-list): Fix docstrings.