[9fans] ftpfs & factotum

[9fans] ftpfs & factotum

[presotto]

I've changed ftpfs to ask factotum for a user name and password.  It
ignores factotum if its talking to a Plan 9 server since the password
there is really an encrypted challenge.  I might fix that in the
future though I'ld rather not have to, there's too much artificial
intelligence in this program already.

If you use the -a option or you don't have a factotum in your name
space or you don't own the factotum in your name space then
ftpfs reverts to its previous behavior, i.e., it prompts you
for user name and password.

Comments welcome, especially if the new behavior breaks something
you do.