Add X509_up_ref function.

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/ssl/ssl_sess.c b/ssl/ssl_sess.c
index 26a3c43..69e6d7f 100644
--- a/ssl/ssl_sess.c
+++ b/ssl/ssl_sess.c
@@ -266,7 +266,7 @@
     dest->references = 1;
 
     if (src->peer != NULL)
-        CRYPTO_add(&src->peer->references, 1, CRYPTO_LOCK_X509);
+        X509_up_ref(src->peer);
 
     if (src->peer_chain != NULL) {
         dest->peer_chain = X509_chain_up_ref(src->peer_chain);