(mm-mime-mule-charset-alist): Use shift_jis instead of iso-2022-jp-2 for the

(mm-mime-mule-charset-alist): Use shift_jis instead of iso-2022-jp-2 for the
 katakana-jisx0201 mule charset;
 add new entries for the mime charsets iso-2022-jp-3 and shift_jis.
(mm-coding-system-priorities): Use shift_jis and iso-8859-1 instead of
 japanese-shift-jis and iso-latin-1 respectively in order to share the default
 value with both Emacs and XEmacs-mule.
(mm-mule-charset-to-mime-charset): Make mm-coding-system-priorities effective.
(mm-sort-coding-systems-predicate): Canonicalize coding-systems while
 predicating of candidates upon the priorities.