$FreeBSD$ tags and man page dates.
Add a post-merge script which reapplies these changes.
Run both scripts to normalize the existing code base. As a result, many
files which should have had $FreeBSD$ tags but didn't now have them.
Partly rewrite the upgrade instructions and remove the now outdated
list of tricks.
I have worked hard to reduce diffs against the vendor branch. One
notable change in that respect is that we no longer prefer DSA over
RSA - the reasons for doing so went away years ago. This may cause
some surprises, as ssh will warn about unknown host keys even for
hosts whose keys haven't changed.
MFC after: 6 weeks
