Update ntp4 package to 4.2.8p8, security fix.

(4.2.8p8) 2016/06/02 Released by Harlan Stenn <stenn@ntp.org>

* [Sec 3042] Broadcast Interleave.  HStenn.
* [Sec 3043] Autokey association reset.  perlinger@ntp.org, stenn@ntp.org
  - validate origin timestamps on bad MACs, too.  stenn@ntp.org
* [Sec 3044] Spoofed server packets are partially processed.  HStenn.
* [Sec 3045] Bad authentication demobilizes ephemeral associations. JPerlinger.
* [Sec 3046] CRYPTO_NAK crash.  stenn@ntp.org
* [Bug 3038] NTP fails to build in VS2015. perlinger@ntp.org
  - provide build environment
  - 'wint_t' and 'struct timespec' defined by VS2015
  - fixed print()/scanf() format issues
* [Bug 3052] Add a .gitignore file.  Edmund Wong.
* [Bug 3054] miscopt.html documents the allan intercept in seconds. SWhite.
* [Bug 3058] fetch_timestamp() mishandles 64-bit alignment. Brian Utterback,
  JPerlinger, HStenn.
* Update the NEWS file for 4.2.8p8.  HStenn.
* Fix typo in ntp-wait and plot_summary.  HStenn.
* Make sure we have an "author" file for git imports.  HStenn.
* Update the sntp problem tests for MacOS.  HStenn.

(taca)