upstream: Add experimental support for PQC XMSS keys (Extended

Hash-Based Signatures) The code is not compiled in by default (see WITH_XMSS
in Makefile.inc) Joint work with stefan-lukas_gazdag at genua.eu See
https://tools.ietf.org/html/draft-irtf-cfrg-xmss-hash-based-signatures-12 ok
djm@

OpenBSD-Commit-ID: ef3eccb96762a5d6f135d7daeef608df7776a7ac
diff --git a/readconf.c b/readconf.c
index 56bff85..88051db 100644
--- a/readconf.c
+++ b/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.282 2018/02/23 02:34:33 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.283 2018/02/23 15:58:37 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1943,6 +1943,7 @@
 #endif
 		add_identity_file(options, "~/",
 		    _PATH_SSH_CLIENT_ID_ED25519, 0);
+		add_identity_file(options, "~/", _PATH_SSH_CLIENT_ID_XMSS, 0);
 	}
 	if (options->escape_char == -1)
 		options->escape_char = '~';