(chise-tex-encode-region-for-utf-8-jis): New optional argument

(chise-tex-encode-region-for-utf-8-jis): New optional argument
`ptex-mode'; don't encode JIS X 0208:1990 characters as the same as
JIS X 0208:1983 characters; don't use \UCSsip{hhhhh} when `ptex-mode'
is t; don't encode JIS X 0213 characters when `ptex-mode' is nil.
(chise-ptex-encode-region-for-utf-8-jis): New function.
(chise-xetex-encode-region-for-utf-8-jis): Add local variable `rest'
and `spec'.
(utf-8-jp-ptex): New coding-system.