Upgrade NTP to 4.2.8p4.

Security: FreeBSD-SA-15:25.ntp
Security: CVE-2015-7871
Security: CVE-2015-7855
Security: CVE-2015-7854
Security: CVE-2015-7853
Security: CVE-2015-7852
Security: CVE-2015-7851
Security: CVE-2015-7850
Security: CVE-2015-7849
Security: CVE-2015-7848
Security: CVE-2015-7701
Security: CVE-2015-7703
Security: CVE-2015-7704, CVE-2015-7705
Security: CVE-2015-7691, CVE-2015-7692, CVE-2015-7702
Approved by: so

Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Let bsd.prog.mk set SRCS and MAN to their default values.

Start the dreaded NOFOO -> NO_FOO conversion.

OK'ed by: core

For variables that are only checked with defined(), don't provide
any fake value.

Perform a major cleanup of the usr.sbin Makefiles.
These are not perfectly in agreement with each other style-wise, but they
are orders of orders of magnitude more consistent style-wise than before.

- remove trace of libkvm. It is not used at all.
- reorganise the Makefiles: the order of variables was not the usual one.

Explained gently by: bde

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)