Two new methods: DnsServer.create_sock(type) and DnsServer.send_raw(data, sock)

Because, it's simple to ask over TCP straight away instead of potential
resolving of truncated responses. For example if the used TSIG key name
is too long.

Such packets shouldn't be treated as DNS at all and should be
processed anyway.

closes #210

DSA does not work well with 0.9.8 and even Debian stable contains 1.0.1.
Intentionally no hard-check in autoconf included.

Not actually used in the code, but was broken.

refs #181

refs #181