RT 1505: Use SSL3_AL_FATAL not "2"

Use SSL3_AL_FATAL instead of the literal constant "2"
Every bit of cleanup helps.
Reviewed-by: Matt Caswell <matt@openssl.org>
diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index 8fc3bb4..9a1d65d 100644
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -1793,7 +1793,7 @@
 		desc = SSL_AD_HANDSHAKE_FAILURE; /* SSL 3.0 does not have protocol_version alerts */
 	if (desc < 0) return -1;
 	/* If a fatal one, remove from cache */
-	if ((level == 2) && (s->session != NULL))
+	if ((level == SSL3_AL_FATAL) && (s->session != NULL))
 		SSL_CTX_remove_session(s->ctx,s->session);
 
 	s->s3->alert_dispatch=1;