(find-coding-systems-for-charsets):

(find-coding-systems-for-charsets):
Handle the case of unknown charset.
(find-multibyte-characters): If invalid multibyte characters are
found, return the corresponding strings instead of character
codes.
(find-multibyte-characters): Adjusted for the above change.
(select-safe-coding-system): For a unibyte buffer, always returns
DEFAULT-CODING-SYSTEM.
(get-charset-property): Fix previous change.  Make it a function.
(put-charset-property): Make it a function.