Connect to old TLSv1.0 software - override new openssl defaults. (#441)

* Connect to old TLSv1.0 software - override new openssl defaults.

Inspired by similar wpa_supplicant bug, triggered by libssl1.1
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=907518#95
  https://w1.fi/cgit/hostap/commit/?id=cc9c4feccc5588137f66c40a4a6729476556853e

* Include openssl/x509.h in addition to openssl/tls1.h

Needed to get the declaration of STACK_OF() in buggy versions of OpenSSL.

* fix building against libressl

libressl uses openssl version numbers between 1 and 2, but does not
yet support tls 1.3, so we can not use TLS1_3_VERSION in that case.