MEDIUM: ssl: Add support for OpenSSL 1.1.0

MEDIUM: ssl: Add support for OpenSSL 1.1.0

In the last release a lot of the structures have become opaque for an
end user. This means the code using these needs to be changed to use the
proper functions to interact with these structures instead of trying to
manipulate them directly.

This does not fix any deprecations yet that are part of 1.1.0, it only
ensures that it can be compiled against that version and is still
compatible with older ones.

[wt: openssl-0.9.8 doesn't build with it, there are conflicts on certain
     function prototypes which we declare as inline here and which are
     defined differently there. But openssl-0.9.8 is not supported anymore
     so probably it's OK to go without it for now and we'll see later if
     some users still need it. Emeric has reviewed this change and didn't
     spot anything obvious which requires special care. Let's try it for
     real now]