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@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@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