TODO
     hostname handling.
     update DHCP6 configs from dns
     parse domain=<domain>,<IPv6 range>
     pretty-print counted string options.
     DECLINE messages
     lease-script fro DHCPv6

stdout and stderr file descriptors open. This can manifest
itself as 100% CPU use. Thanks to Chris Moore for finding
this.

duplicate address code, since we're now searching a temporary hash
which holds only F_HOST records.

Use the packet buffer for hash-buckets, better hash function.