MFC r319487-r319488, r319682, r319968, r319995

r319487:
Add VNC Authentication support based on RFC6143 section 7.2.2.

Submitted by: Fabian Freyer <fabian.freyer@physik.tu-berlin.de>
Reworked by: myself
Reviewed by: grehan, rgrimes and jilles
Relnotes: Yes.
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D10818

r319488:
Bump manpage date.

r319682:
Make the VNC authentication build with LibreSSL on HardenedBSD and TrueOS.

PR: 219790
Submitted by: Shirkdog <mshirk@daemon-security.com>
Reviewed by: grehan and rgrimes
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D11071

r319968:
Initialize variables and use byteorder(9) instead of aliasing char array
buf via uint32_t pointer.

CID: 1375949
Reported by: Coverity, cem
Reviewed by: cem
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D11153

r319995:
Check if pthread_create(3) successfully created the thread prior to call
pthread_join(3). The variable tid is not yet initialized in case
the authentication fails at early stage, that would lead pthread_join be
called with an uninitialized variable.

CID: 1375950
Reported by: Coverity, cem
Reviewed by: cem
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D11150