Fix doc strings in ispell.el/.
lisp/textmodes/ispell.el (ispell-skip-tib, ispell-keep-choices-win)
(ispell-choices-win-default-height, ispell-silently-savep)
(ispell-dictionary-alist, ispell-encoding8-command)
(ispell-check-version, ispell-aspell-find-dictionary)
(ispell-valid-dictionary-list, ispell-words-keyword)
(ispell-get-word, ispell-internal-change-dictionary)
(ispell-region, ispell-skip-region-list)
(ispell-begin-skip-region-regexp, ispell-ignore-fcc)
(ispell-process-line, ispell-minor-mode, ispell-minor-check)
(ispell-message-text-end, ispell-message)
(ispell-buffer-local-parsing): Doc fix.