Converts thing into a pathname.
The host supplies a host name with respect to which the parsing occurs.
If thing is a stream associated with a file,
processing proceeds as if the pathname used to open that file
had been supplied instead.
If thing is a pathname,
the host and the host component of thing are compared.
If they match,
two values are immediately returned: thing and start;
otherwise (if they do not match), an error is signaled.
Otherwise (if thing is a string),
parse-namestring parses the name of a file within
the substring of thing bounded by start and end.
If thing is a string then
the substring of thing bounded by start and end
is parsed into a pathname
In the first
the host portion of the logical pathname namestring
and its following colon are optional.
If the host portion of the namestring and host
are both present and do not match,
an error is signaled.
If junk-allowed is true,
then the primary value is the pathname parsed
or, if no syntactically correct pathname was seen, nil.
If junk-allowed is false,
then the entire substring is scanned,
and the primary value is the pathname parsed.
In either case, the secondary value
is the index into thing of the delimiter that terminated the parse,
or the index beyond the substring if the parse terminated at the end of the substring
(as will always be the case if junk-allowed is false).
Parsing a null string always succeeds,
producing a pathname with all components (except the host) equal to nil.
If thing contains an explicit host name and no explicit device name,
then it is implementation-defined whether parse-namestring
will supply the standard default device for that host as the device component
of the resulting pathname.