[MINOR] add basic signal handling functions

These functions will be used to deliver asynchronous signals in order
to make the signal handling functions more robust. The goal is to keep
the same interface to signal handlers.
diff --git a/include/types/signal.h b/include/types/signal.h
new file mode 100644
index 0000000..b863d23
--- /dev/null
+++ b/include/types/signal.h
@@ -0,0 +1,20 @@
+/*
+ * Asynchronous signal delivery functions descriptors.
+ *
+ * Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <signal.h>
+#include <common/config.h>
+#include <common/standard.h>
+
+struct signal_descriptor {
+	int count;  /* number of times raised */
+	void (*handler)(int sig);
+};