openssl: move SSLSocket#initialize to C extension

* ext/openssl/lib/openssl/ssl.rb (SSLSocket): Move the implementation of
  SSLSocket#initialize to C. Initialize the SSL (OpenSSL object) in it.
  Currently this is delayed until ossl_ssl_setup(), which is called from
  SSLSocket#accept or #connect. Say we call SSLSocket#hostname= with an
  illegal value. We expect an exception to be raised in #hostname= but
  actually we get it in the later SSLSocket#connect. Because the SSL is
  not ready at #hostname=, the actual call of SSL_set_tlsext_host_name()
  is also delayed.
  This also fixes: [ruby-dev:49376] [Bug #11724]

* ext/openssl/ossl_ssl.c (ossl_ssl_initialize): Added. Almost the same
  as the Ruby version but this instantiate the SSL object at the same
  time.

  (ossl_ssl_setup): Adjust to the changes. Just set the underlying IO to
  the SSL.

  (ssl_started): Added. Make use of SSL_get_fd(). This returns -1 if not
  yet set by SSL_set_fd().

  (ossl_ssl_data_get_struct): Removed. Now GetSSL() checks that the SSL
  exists.

  (ossl_ssl_set_session): Don't call ossl_ssl_setup() here as now the
  SSL is already instantiated in #initialize.

  (ossl_ssl_shutdown, ossl_start_ssl, ossl_ssl_read_internal,
   ossl_ssl_write_internal, ossl_ssl_stop, ossl_ssl_get_cert,
   ossl_ssl_get_peer_cert, ossl_ssl_get_peer_cert_chain,
   ossl_ssl_get_version, ossl_ssl_get_cipher, ossl_ssl_get_state,
   ossl_ssl_pending, ossl_ssl_session_reused,
   ossl_ssl_get_verify_result, ossl_ssl_get_client_ca_list,
   ossl_ssl_npn_protocol, ossl_ssl_alpn_protocol, ossl_ssl_tmp_key): Use
  GetSSL() instead of ossl_ssl_data_get_struct(). Use ssl_started().

  (Init_ossl_ssl): Add method declarations of SSLSocket#{initialize,
  hostname=}.

* ext/openssl/ossl_ssl.h (GetSSL): Check that the SSL is not NULL. It
  should not be NULL because we now set it in #initialize.

* ext/openssl/ossl_ssl_session.c (ossl_ssl_session_initialize): No need
  to check if the SSL is NULL.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55191 b2dd03c8-39d4-4d8f-98ff-823fe69b080e