There are several variants of "libtap" floating around the net, many of which
are derived from the one by Nik Clayton, as is this one.

This one is based on CCAN's: http://ccodearchive.net/info/tap.html

It has been modified to suit gdnsd's build setup, which includes a few
compiler things, warnings fixes, and removal of the tap fail callback stuff,
but is otherwise as fetched from the CCAN repo circa Nov 10, 2014 at git rev
291237b4.
