Let nl_langinfo(CODESET) return "US-ASCII" as the name of the

Let nl_langinfo(CODESET) return "US-ASCII" as the name of the
character codeset for the POSIX/C default locale.  This is the
preferred IANA name and also used by FreeBSD.

The previous value "646" was an obscure reference to ISO 646 (= ASCII)
and was not recognized by GNU iconv out of the box.

ok millert@, stsp@