psql binary output

I whipped this up some months ago and forgot that I hadn't sent in the
patch.

This implements two psql commands: \gb and \gbn

Both fetch and output results in binary mode - \gb uses separators,
while \gbn does not. Examples:

[andrew(at)emma inst.psql-binout.5705]$ echo "select bytea '\\x00010203', bytea '\\x040506' \\gbn" | bin/psql | od -c
0000000 \0 001 002 003 004 005 006
0000007
[andrew(at)emma inst.psql-binout.5705]$ echo "select bytea '\\x00010203', bytea '\\x040506' \\gb" | bin/psql | od -c
0000000 \0 001 002 003 | 004 005 006 \n
0000011

This is an attempt to deal with the question I originally posed here:
<http://people.planetpostgresql.org/andrew/index.php?/archives/196-Clever-trick-challenge.html>
and is based on a suggestion Tom later made (although anything wrong
here is of course my fault, not his.

If people are interested I'll try to finish this up and document it.

cheers

andrew