src/, client/: Use the new adns_text2addr/addr2text functions.

The sortlist is now IPv6 aware.  The nameserver configuration could cope
with IPv6 addresses, but the transport machinery can't, so we pick them
out by hand.  PTR reverse-query handling still doesn't do anything
special, because we don't have AAAA query support yet.

I've also hacked adnshost's `-i' and `--reverse' options to use the new
functions, and they'll accept IPv6 addresses, but the underlying
adns_submit_reverse machinery will reject them still.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>