add a random sleep of up to half an hour to distribute the server

load from spamd-setup. Brought up by phessler@ who also pointed out
that the percent sign must be escaped in the command.
ok ajacoutot@ joerg@ phessler@ and sort of @blambert

src/etc/crontab

@@ -1,4 +1,4 @@
-#	$OpenBSD: crontab,v 1.18 2009/05/09 17:15:49 schwarze Exp $
+#	$OpenBSD: crontab,v 1.19 2013/10/19 15:26:06 halex Exp $
 #
 # /var/cron/tabs/root - root's crontab
 #
@@ -20,4 +20,4 @@ HOME=/var/log
 30	1	*	*	*	/bin/sh /etc/daily
 30	3	*	*	6	/bin/sh /etc/weekly
 30	5	1	*	*	/bin/sh /etc/monthly
-#0	*	*	*	*	/usr/libexec/spamd-setup
+#0	*	*	*	*	sleep $((RANDOM \% 1800)) && /usr/libexec/spamd-setup