(tm-eword::space-process): Don't concatenate `special's.

(tm-eword::space-process): Don't concatenate `special's.
(ew-encode-rword-1): Renamed from `tm-eword::encode-string-1'; add new
optional argument `must-output'; return nil if it can't encode
literally.
(eword-encode-rword-list): Fold SPACE or TAB in the encoded string if
`ew-encode-rword-1' can't encode literally and it is possible to
encode the rest literally with the folding.
(eword-encode-phrase-to-rword-list): Add `special' flag to brackets of
comments.