* Get NATIVE-NAMESTRING to do all and only the desired things for all
accepted non-wild NAME and TYPE components. Add a few tests for
these cases.
* Add new user-visible features to PARSE-NATIVE-NAMESTRING and
NATIVE-NAMESTRING for parsing/unparsing things "as files" or "as
directories"; these are convenient for use with SB-POSIX, and will
be handy in a few places in SBCL's internals, too.