If possible don't use forwarders when priming the resolver.

If we try to fetch a record from cache and need to look into
hints database we assume that the resolver is not primed and
start dns_resolver_prime(). Priming query is supposed to return
NSes for "." in ANSWER section and glue records for them in
ADDITIONAL section, so that we can fill that info in 'regular'
cache and not use hints db anymore.
However, if we're using a forwarder the priming query goes through
it, and if it's configured to return minimal answers we won't get
the addresses of root servers in ADDITIONAL section. Since the
only records for root servers we have are in hints database we'll
try to prime the resolver with every single query.

This patch adds a DNS_FETCHOPT_NOFORWARD flag which avoids using
forwarders if possible (that is if we have forward-first policy).
Using this flag on priming fetch fixes the problem as we get the
proper glue. With forward-only policy the problem is non-existent,
as we'll never ask for root server addresses because we'll never
have a need to query them.

Also added a test to confirm priming queries are not forwarded.

bin/tests/system/forward/ns4/named.conf.in

@@ -19,6 +19,7 @@ options {
 	listen-on-v6 { none; };
 	recursion yes;
 	dnssec-validation yes;
+	minimal-responses yes;
 };
 
 zone "." {

bin/tests/system/forward/ns7/named.conf.in

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+options {
+	query-source address 10.53.0.7;
+	notify-source 10.53.0.7;
+	transfer-source 10.53.0.7;
+	port @PORT@;
+	pid-file "named.pid";
+	listen-on { 10.53.0.7; };
+	listen-on-v6 { none; };
+	forwarders { 10.53.0.4; };
+	forward first;
+	dnssec-validation yes;
+};
+
+zone "." {
+	type hint;
+	file "root.db";
+};

bin/tests/system/forward/ns7/root.db

@@ -0,0 +1,28 @@
+; Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+;
+; This Source Code Form is subject to the terms of the Mozilla Public
+; License, v. 2.0. If a copy of the MPL was not distributed with this
+; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;
+; See the COPYRIGHT file distributed with this work for additional
+; information regarding copyright ownership.
+
+$TTL 300
+. 			IN SOA	gson.nominum.com. a.root.servers.nil. (
+				2000042100   	; serial
+				600         	; refresh
+				600         	; retry
+				1200    	; expire
+				600       	; minimum
+				)
+.			NS	a.root-servers.nil.
+a.root-servers.nil.	A	10.53.0.1
+
+example1		NS	ns.example1
+ns.example1		A	10.53.0.1
+
+example2		NS	ns.example2
+ns.example2		A	10.53.0.1
+
+example3		NS	ns.example3
+ns.example3		A	10.53.0.1

bin/tests/system/forward/setup.sh

@@ -18,3 +18,4 @@ copy_setports ns2/named.conf.in ns2/named.conf
 copy_setports ns3/named.conf.in ns3/named.conf
 copy_setports ns4/named.conf.in ns4/named.conf
 copy_setports ns5/named.conf.in ns5/named.conf
+copy_setports ns7/named.conf.in ns7/named.conf

bin/tests/system/forward/tests.sh

@@ -147,5 +147,17 @@ if [ $sent -ne 1 ]; then ret=1; fi
 if [ $ret != 0 ]; then echo_i "failed"; fi
 status=`expr $status + $ret`
 
+echo_i "checking that priming queries are not forwarded"
+ret=0
+$DIG $DIGOPTS +noadd +noauth txt.example1. txt @10.53.0.7 > dig.out.f7 || ret=1
+sent=`sed -n '/sending packet to 10.53.0.1/,/^$/p' ns7/named.run | grep ";.*IN.*NS" | wc -l`
+[ $sent -eq 1 ] || ret=1
+sent=`grep "10.53.0.7#.* (.): query '\./NS/IN' approved" ns4/named.run | wc -l`
+[ $sent -eq 0 ] || ret=1
+sent=`grep "10.53.0.7#.* (.): query '\./NS/IN' approved" ns1/named.run | wc -l`
+[ $sent -eq 1 ] || ret=1
+if [ $ret != 0 ]; then echo_i "failed"; fi
+status=`expr $status + $ret`
+
 echo_i "exit status: $status"
 [ $status -eq 0 ] || exit 1