[9fans] upas contrib package

[erik quanstrom <quanstro@quanstro.net>]

i've rolled all the upas changes into a contrib package,
quanstro/nupas.  unfortunately, it's not as clean an
installation as i would like.  i'm sure there will be some
rough edges.  problems reports and suggestions for cleaning
things up are welcome.

there is a few steps to prepare for this package.

	; mv /sys/src/cmd/upas /sys/src/cmd/oupas
	; mv /386/bin/upas /386/bin/oupas
	; mkdir /386/bin/upas

once installed, you'll either (a) need to change /lib/profile
as follows. add the marked line

	# standard bin
>>	bind /$cputype/bin/nupas /$cpu/bin/upas
	bind /$cputype/bin /bin

or (b) use the script usenupas anywhere upas is called.  this
will be necessary for smtp, smtpd, imap4d, etc.

finally, take a look at validatesender.  nupas smtpd
passes some extra arguments to /mail/lib/validatesender
to facilitate spf and spamhaus checks.  the version provided
insists that both spf and spamhaus check out.  alternately
one could use spamhaus only on spf fail or neutral.
i have a vague recollection of a large pile of spam that
passed spf checks so i haven't don that.

- erik