OpenSSL: Use SSL_MODE_RELEASE_BUFFERS if available, reduces memory use

See also :
http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html
http://www.imperialviolet.org/2010/06/25/overclocking-ssl.html

Signed-off-by: Cristian Rodríguez <crrodriguez@opensuse.org>

lib/ssluse.c

@@ -1489,6 +1489,10 @@ ossl_connect_step1(struct connectdata *conn,
     return CURLE_OUT_OF_MEMORY;
   }
 
+#ifdef SSL_MODE_RELEASE_BUFFERS
+  SSL_CTX_set_mode(connssl->ctx, SSL_MODE_RELEASE_BUFFERS);
+#endif
+
 #ifdef SSL_CTRL_SET_MSG_CALLBACK
   if(data->set.fdebug && data->set.verbose) {
     /* the SSL trace callback is only used for verbose logging so we only