upstream: Add server support for signalling sessions via the SSH

channel/ session protocol. Signalling is only supported to sesssions that are
not subsystems and were not started with a forced command.

Long requested in bz#1424

Based on a patch from markus@ and reworked by dtucker@;
ok markus@ dtucker@

OpenBSD-Commit-ID: 4bea826f575862eaac569c4bedd1056a268be1c3
diff --git a/session.h b/session.h
index 54dd1f0..ce59dab 100644
--- a/session.h
+++ b/session.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: session.h,v 1.35 2017/09/12 06:32:07 djm Exp $ */
+/* $OpenBSD: session.h,v 1.36 2018/10/02 12:40:07 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -35,6 +35,7 @@
 	struct passwd *pw;
 	Authctxt *authctxt;
 	pid_t	pid;
+	int	forced;
 
 	/* tty */
 	char	*term;