Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFH (r237568, r255422, r255460, r255766, r255767, r255774, r255829,
r256126, r257954, r261320, r261499, r263691, r263712): upgrade to
OpenSSH 6.6p1 via 6.3p1, 6.4p1 and 6.5p1.

Differences relative to head:

- No DNSSEC support since stable/9 does not have LDNS
- Sandboxing off by default, and uses rlimit instead of Capsicum
- ED25519 moved to the bottom of the order of preference to avoid
"new public key" warnings

Upgrade to OpenSSH 6.5p1.

Vendor import of OpenSSH 6.5p1.