Doc fixes.

Doc fixes.
(top-level): Don't add hooks here.
(whitespace-running-emacs): Deleted.
(timer): Don't require.
(whitespace): Add back :version conditional on xemacs test.
(whitespace-spacetab-regexp, whitespace-indent-regexp)
(whitespace-ateol-regexp, whitespace-modes): Fix custom type.
(whitespace-force-mode-line-update, whitespace-refresh-rescan-list)
(whitespace-tickle-timer, whitespace-rescan-files-in-buffers):
Avoid specific xemacs test.
(whitespace-global-mode): New option.
(whitespace-global-mode): New command.
(whitespace-unload-hook): New function.