Clean up logging of security information a bit:

Clean up logging of security information a bit:

o Introduce /var/log/authentication.log, which will be the target for
  auth.info and authpriv.info by default.  Rotate on the same schedule
  as most other logs.  Create at installation.

o Remove logging of auth.info from /var/log/security.log, which will
  return to being only for security feature subsystems (such as ipfw,
  and so on).

This creates a special authentication log, which can now be searched
by scripts for authentication events.