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

MFC r259973:

Tighten default restrictions for ntpd(8) server and provide a link
to NTP access restriction documentation.

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

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

As of r232844 we no longer need the maxpoll 9 workaround.

MFC after: 3 days

1) Use our vendor domain at the pool.
2) Point people at the pool website and encourage
people to provide a server in the pool (as a
courtesy to the pool guys).
3) Fix a spelling.
4) Comment out the local clock and include a link
to documentation for use of the local clock on
the ntp.org site.

Approved by: re (kib)

Welcome to a default installed /etc/ntp.conf

This NTP configuration file points to the [012].pool.ntp.org servers,
which will return a list of geographical local NTP servers.
It uses the best-practice options of "iburst" and "maxpoll 9".
It gives examples on how to use the "restrict" commands, which are
unfortunately not working when you use the pool.ntp.org servers.
It sets up a fudge server so any clients syncing against this server
will always be synced even if we lose the master.

The idea of this file was briefly discussed on -net.

PR: conf/58595
Submitted by: Chris Stenton <jacs@gnome.co.uk>
MFC after: 1 week