mcs-e20.el (coding-system-to-mime-charset): Check coding-system-to-mime-charset-exclude-regexp is non-nil.
mcs-e20.el, mcs-xm.el (mime-charset-list): Fix the case that MIME charset and coding system have n:1 relation.
mcs-20.el (detect-mime-charset-string, detect-mime-charset-region): (Emacs23 and later) Refactored to build a list of unique characters without full list of characters in string or region.  Use detect-mime-charset-list.
mcs-20.el (detect-mime-charset-region, detect-mime-charset-string): (Emacs23 and later) Use it.  When `detect-mime-charset-from-coding-system' is non-nil, detect MIME charset by encodability in destination coding system.