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

Pull in all the OpenSSH bits that we'd previously left out because we
didn't use them. This will make future merges from the vendor tree much
easier.

Approved by: re (gjb)

Since we automatically set svn:eol-style on new files (including files
added during a vendor import), set it on the entire dist tree.

svn:keywords is not appropriate for vendor trees.

Properly flatten openssh/dist.

Revert part of 180714 - the intent was to flatten dist, not to nuke it.

Vendor import of OpenSSH 4.3p1.

Vendor import of OpenSSH 3.9p1.