A reimplementation of the NTP protocol daemon and tools in a secure way.

A major new feature is that it implements IETF's Network Time Security standard
for strong cryptographic authentication of time service.

Security improvements:
* Network Time Security is implemented.
* The deprecated ntpdc utility, long a chronic locus of security
  vulnerabilities, has been removed
* Autokey is not supported; that code has been removed, as it was chronically
  prone to security vulnerabilities.
* Peer mode has been removed. The keyword peer in ntp.conf is now just an alias
  for keyword server.
* Broadcast- and multicast modes, which are impossible to secure, have been
  removed.
* The authentication requirement for remote configuration commands (e.g., via
  ntpq) can no longer be disabled.
* The deprecated and vulnerability-prone ntpdate program has been replaced with
  a shell wrapper around ntpdig.