* gnus-art.el (gnus-mime-inline-part): Decode parts according to the coding

* gnus-art.el (gnus-mime-inline-part): Decode parts according to the coding
 cookies; decompress compressed parts.

* mml.el (mml-generate-mime-1): Add the charaset parameter according to the
 value which a user specified manually or the coding cookie.

* mm-util.el (mm-string-to-multibyte): New function.
(mm-detect-mime-charset-region): Work with Emacs 22 as well.
(mm-coding-system-to-mime-charset): New function.
(mm-decompress-buffer): New function.
(mm-find-buffer-file-coding-system): New function.

* mm-view.el (mm-insert-inline): Make sure a part ends with a newline.
(mm-display-inline-fontify): Rewrite for decoding and decompressing parts.