First NTS code

[Eric S. Raymond]

I have broken ground on the NTS code.  It's a set of stubs in the new
file ntpd/nts.c and external declarations in include/nts.h.

None of this is hooked into the rest of the code yet. My intent is to
develop a clean interface that seals the guts of NTS away from the
rest of the code.  Those of you who have been working on nts.adoc
should audit to check that the defined interface is sufficient.

I expect this module to be used by ntpd and a small ntske server
daemon. Because I don't believe incremental code is coing to be an
issue in any of our deployments, I've chosen an organization that
minimizes the exposed API and keeps both client and server NTS code in
one file for maintainability, rather than one that tries to partition
it so that neither deployment sees code unique to the other.

Ueful comments will be those pointing out if this interface fails to
capture any transaction steps described in the RFC, or that the
implied data flow to/from the rest of ntpd needs to change.  It's not
time to argue about policy or implementation details in the code just
yet; for now that conversation should continue as edits to nts.adoc.

While the rest of you look at this and respond, I will be doing
the necessary changes to the configuration parser so it can supply the
parameters needed by the module.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

"Guard with jealous attention the public liberty.  Suspect every one
who approaches that jewel.  Unfortunately, nothing will preserve it
but downright force.  Whenever you give up that force, you are
inevitably ruined."	-- Patrick Henry, speech of June 5 1788