libevent fixup required for Debian 4 (Etch)

Also missing copyright for copied macros.
Fix by Antony Curtis.

extra/libevent/event-internal.h

@@ -70,6 +70,11 @@ struct event_base {
 
 /* Internal use only: Functions that might be missing from <sys/queue.h> */
 #ifndef HAVE_TAILQFOREACH
+/* These following macros are copied from BSD sys/queue.h
+   Copyright (c) 1991, 1993, The Regents of the University of California.
+   All rights reserved.
+*/
+#define	TAILQ_EMPTY(head)		((head)->tqh_first == NULL)
 #define	TAILQ_FIRST(head)		((head)->tqh_first)
 #define	TAILQ_END(head)			NULL
 #define	TAILQ_NEXT(elm, field)		((elm)->field.tqe_next)