Another renegotiation patch

[Simon Josefsson]

Steve, Nikos, are you happy with the safe renegotiation implementation
in git master now?  Do we have complete self-tests of this?  Is it
documented?  Has there been any interop testing with other
implementations?  Any other concerns I should be aware of?

I'd like to release 2.10.0 soon, and safe renegotiation will be one of
the main features in that release.

/Simon