[Pianod] Autoconf round 3

[Perette Barella]

I had another bash at confiscating today, and added some additional tests (IPv6, MSG_NOSIGNAL vs SO_NOSIGPIPE), and updated the C files to actually read all the autconf-generated config.h.

Problem reports appreciated.  If all is quiet, I'm going to assume all is well and commit this to source control the 24th.

Incidentally, if anyone ever needs to do this kind of thing... I recommend "Autotools: A Practitioner's Guide to..." by John Calcote as a fantastic book to bring you up to speed.

Perette