[rbldnsd] ipv6 support: beginnings of an ip6trie dataset

[Michael Tokarev]

Ok. We have a rather busy period for some reason not under our control,
so it took a bit too long.

I merged everything from you into the main branch, added a few very
minor changes on top, and tested the whole thing a bit - mainly on
several different architectures.

In particular, I ran - just the trie selftest! - on armhf, armel,
sparc and powerpc machines, and it all worked fine.  I had no way
to run python tests on there, unfortunately, so if we want to
perform more serious testing, it is still in the TODO list ofcourse.

Now I want to perform a few tests for loading speed, memory usage
and query speed, comparing various options.  For that I want to
grab some real DNSBL data (such as CBL and Spamhaus), because, as
it turned out, "random" data tend to show different results than
reality :)  I want to make these tests this week.

Also, It'd be interesting to instrument the code to perform some
stats wrt reallocs and "wasted" memory, I also want to do it this
week.

But I like what is there very much already, the code is clean and
nice and works pretty well.  Something which I obviously failed to
do so far... ;)

Thank you!

/mjt