[v9_10] DDoS mitigation features

3938.	[func]		Added quotas to be used in recursive resolvers
			that are under high query load for names in zones
			whose authoritative servers are nonresponsive or
			are experiencing a denial of service attack.

			- "fetches-per-server" limits the number of
			  simultaneous queries that can be sent to any
			  single authoritative server.  The configured
			  value is a starting point; it is automatically
			  adjusted downward if the server is partially or
			  completely non-responsive. The algorithm used to
			  adjust the quota can be configured via the
			  "fetch-quota-params" option.
			- "fetches-per-zone" limits the number of
			  simultaneous queries that can be sent for names
			  within a single domain.  (Note: Unlike
			  "fetches-per-server", this value is not
			  self-tuning.)
			- New stats counters have been added to count
			  queries spilled due to these quotas.

			These options are not available by default;
			use "configure --enable-fetchlimit" (or
			--enable-developer) to include them in the build.

			See the ARM for details of these options. [RT #37125]

bin/tests/system/fetchlimit/prereq.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+#
+# Copyright (C) 2015  Internet Systems Consortium, Inc. ("ISC")
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+# AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+# OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+# PERFORMANCE OF THIS SOFTWARE.
+
+SYSTEMTESTTOP=..
+. $SYSTEMTESTTOP/conf.sh
+
+if ./fetchlimit
+then
+    :
+else
+    echo "I:This test requires --enable-fetchlimit at compile time." >&2
+    exit 255
+fi
+
+if $PERL -e 'use Net::DNS;' 2>/dev/null
+then
+    if $PERL -e 'use Net::DNS; die if ($Net::DNS::VERSION >= 0.76 && $Net::DNS::VERSION <= 0.77);' 2>/dev/null
+    then
+	:
+    else
+	echo "I:Net::DNS version 0.76 and 0.77 have a bug that causes this test to fail: please update." >&2
+	exit 1
+    fi
+else
+    echo "I:This test requires the Net::DNS library." >&2
+    exit 1
+fi