Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Please welcome the brand new ntp4 daemon & utilities in the FreeBSD tree.
This is the second part of the commit (the third -- link in usr.sbin/Makefile)
will be done after a more complete review by phk & obrien.

NOTE: the number of drivers included in the default configuration is very
minimal, mainly local clocks and the one I use RAWDCF. Anyone wanting to
have a more complete version will find recompilation very easy.

It builds and runs on both alpha & i386. It also does survive "make world".

Reviewed by: phk, obrien (partly)