[9fans] allowing space (ASCII 0x20) in file names

[forsyth@caldo.demon.co.uk forsyth@caldo.demon.co.uk]

i've done various forms of nntp support, client and server, without too much trouble.
getting a reliable feed was rather more of a problem, as was the volume,
and the volume of noise.

once when i had to worry about conveying names with spaces (x.400 addresses)
i used iso no-break space (+U'00A0' i think).  it was adequate,
which is more than i can say for some of the RFCs i've read or had
to implement over the years.  i found i nearly always had to check
someone else's code to see what clients or servers actually expected.
implement the rfc precisely (or as accurately as you can determine it),
and you often hit problems.

pop3 is one example:  several famous clients made undocumented assumptions
(i think one was `there is a space following +OK').
spaces and file name lengths were the least of my problems.

i'm surprised that nfs requires that the underlying file system
actually have links, as opposed to rejecting requests to form or manipulate
them (especially given that there are valid reasons for refusing such
requests even on file systems that have got links).