sshd - Change options defaults to be more secure

sshd - Change options defaults to be more secure

* Change the password_authentication default to 0.  Passworded logins
  are NOT considered secure by default in DragonFly.

* Put in a succinct comment for both the pam default (0) and the
  password authentication default (also 0) to try to prevent them
  from being improper changed back to 1 accidently.