OpenBSD: fix tar command.

Makefile.am

@@ -24,7 +24,7 @@ install-conf:
 
 install-rules:
 	install -d $(e_sysconfdir)/rules
-	wget -qO - http://rules.emergingthreats.net/open/suricata/emerging.rules.tar.gz | tar zkx -C $(e_sysconfdir)
+	wget -qO - http://rules.emergingthreats.net/open/suricata/emerging.rules.tar.gz | tar -x -z -C $(e_sysconfdir) -f -
 	@test -e $(e_sysconfdir)/rules/decoder-events.rules || install -m 600 $(top_srcdir)/rules/decoder-events.rules $(e_sysconfdir)/rules/
 	@test -e $(e_sysconfdir)/rules/stream-events.rules || install -m 600 $(top_srcdir)/rules/stream-events.rules $(e_sysconfdir)/rules/
 	@test -e $(e_sysconfdir)/rules/smtp-events.rules || install -m 600 $(top_srcdir)/rules/smtp-events.rules $(e_sysconfdir)/rules/