(ispell-region): Take acount of the fact that `ispell'

(ispell-region): Take acount of the fact that `ispell'
will return OFFSET by counting non-ASCII characters as one.
(ispell-dictionary-alist-1): Add coding systems to each entry.
(ispell-dictionary-alist-2): Likewise.
(ispell-get-coding-system): New function.
(ispell-decode-string): New function.
(ispell-get-casechars): Decode the string if necessary.
(ispell-get-not-casechars, ispell-get-otherchars): Likewise.