QSslSocket must support TLS 1.3.

Making Qt's OpenSSL 1.1 to build with OpenSSL 1.1.1 seems to be trivial - a matter of fixing openssl.cpp in config.tests + small changes in code. But this is apparently a delusion, looking at this: https://www.openssl.org/blog/blog/2018/02/08/tlsv1.3/ things are not that simple. A bunch of failing auto-tests only confirms - it's not just cosmetics. Thus it would be smart to investigate/research what changes we need to the existing code in advance, before it (OpenSSL 1.1.1 with TLS v. 1.3 support) is finally released.