If the result of a SSL_{CTX_,}set_{min,max}_proto_version() call
leaves the min and max version identical, and support for that version
is compiled out of the library, return an error.  Such an object has
no hope of successfully completing a handshake, and this error may
be easier to decipher than the resulting handshake failure.

Reviewed-by: Rich Salz <rsalz@openssl.org>

(cherry picked from commit c8feba7)

Updated the cherry-pick to not reference TLS1_3_VERSION, which does
not exist on this branch.

(Merged from #4376)

OpenSSL 1.1.0 made SSL_CTX and SSL structs opaque and introduced a new
API to set the minimum and maximum protocol version for SSL_CTX with
TLS_method(). Add getters to introspect the configured versions:

  int SSL_CTX_get_min_proto_version(SSL_CTX *ctx);
  int SSL_CTX_get_max_proto_version(SSL_CTX *ctx);
  int SSL_get_min_proto_version(SSL *ssl);
  int SSL_get_max_proto_version(SSL *ssl);

NOTE: The getters do not resolv the version in case when the minimum or
maxium version are configured as '0' (meaning auto-select lowest and
highst version number).

Signed-off-by: Christian Heimes <christian@python.org>

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>

(cherry picked from commit 3edabd3)

Updated for new manual page location and TLS 1.3.

(Merged from #4376)