better dns

[presotto@plan9.bell-labs.com presotto@plan9.bell-labs.com]

Our current dns is now in {ftp|http}://plan9.bell-labs.com/plan9/update/ndb.
The file

	ndb.tar.xor

is a tar of the directory /sys/src/cmd/ndb xor'd with
the file /68020/9gnot from the sold CD.  The files

	v.xor
	8.xor
	k.xor
	2.xor

are programs that will xor 2 files.  To recover the
original tar file on a 386:

	8.xor ndb.tar.xor /68020/9gnot

Its hokey but it should work as long as none of the
people that bought the CD don't post the /68020/9gnot
file.

This dns makes a much better server than the old one did.  It
caches all the local info in the program's address space when
running as a server.  Oodles of bugs are gone.  The dnstcp program
answers zone transfer requests.  This program is currently
what is serving the bell-las.com domain.

Included is also a dnsdebug program that helps debug dns problems.
The interface is the same as dnsquery except that lines starting
with @ redirect the query to that server, e.g.

@achille.cs.bell-labs.com boofhead.com mx

will ask achille.cs.bell-labs.com for an mx record for boofhead.com.

Complaints to me.