Alow quoting of user, group, and last modifier IDs.

These changes nescessary for the CIFS client and p9p for Windows as their
user/group/domain names often contain whitespace.

Also, string literals are put in readonly memory on windows so ls(".") causes
a suicide when xcleanname() modifies the string needlessly, xcleanname modified
not to touch the string unless necessary.

I am fairly sure this will be sorry'ed but at least it will be
on sources if anyone has similar problems.

-Steve