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.