MFH (r314306,r314720): Upgrade OpenSSH to 7.4p1.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Upgrade to OpenSSH 6.8p1.

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)

Vendor import of OpenSSH 6.1p1.

Vendor import of OpenSSH 5.5p1

Oops, remove svn:keyword again.

Vendor import of OpenSSH 4.6p1 for posterity's sake