Initial "opaque SSL" framework. If an application defines OPENSSL_NO_SSL_INTERN

Initial "opaque SSL" framework. If an application defines OPENSSL_NO_SSL_INTERN
all ssl related structures are opaque and internals cannot be directly
accessed. Many applications will need some modification to support this and
most likely some additional functions added to OpenSSL.

The advantage of this option is that any application supporting it will still
be binary compatible if SSL structures change.

(backport from HEAD).