BUG/MEDIUM: connections: Always add the xprt handshake if needed.

In connect_server(), we used to only call xprt_add_hs() if CO_FL_SEND_PROXY
was set during the function call, we would not do it if the flag was set
before connect_server() was called. The rational at the time was if the flag
was already set, then the XPRT was already present. But now the xprt_handshake
always removes itself, so we have to re-add it each time, or it wouldn't be
done if the first connection attempt failed.
While I'm there, check any non-ssl handshake flag, instead of just
CO_FL_SEND_PROXY, or we'd miss the SOCKS4 flags.

This should be backported to 2.0.
diff --git a/src/backend.c b/src/backend.c
index bff71ab..37a67c9 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1213,7 +1213,6 @@
 	int reuse_orphan = 0;
 	int init_mux = 0;
 	int alloced_cs = 0;
-	int flags_hs = 0;
 	int err;
 
 
@@ -1484,7 +1483,6 @@
 			return SF_ERR_INTERNAL;
 	}
 
-	flags_hs = srv_conn->flags & CO_FL_HANDSHAKE_NOSSL;
 	if (!conn_xprt_ready(srv_conn) && !srv_conn->mux) {
 		/* set the correct protocol on the output stream interface */
 		if (srv)
@@ -1595,7 +1593,7 @@
 	/* The CO_FL_SEND_PROXY flag may have been set by the connect method,
 	 * if so, add our handshake pseudo-XPRT now.
 	 */
-	if (!flags_hs && (srv_conn->flags & CO_FL_SEND_PROXY)) {
+	if ((srv_conn->flags & CO_FL_HANDSHAKE_NOSSL)) {
 		if (xprt_add_hs(srv_conn) < 0) {
 			conn_full_close(srv_conn);
 			return SF_ERR_INTERNAL;