in iconv_open, accept "CHAR" and "" as aliases for "UTF-8"

in iconv_open, accept "CHAR" and "" as aliases for "UTF-8"

while not a requirement, it's common convention in other iconv
implementations to accept "CHAR" as an alias for nl_langinfo(CODESET),
meaning the encoding used for char[] strings in the current locale,
and also "" as an alternate form. supporting this is not costly and
improves compatibility.