check 'rndc recursing'

there was no system test that exercised 'rndc recursing'; a
simple one has now been added; it confirms that the number of
recursing clients reported by 'rndc stats' is in agreement with
the list returned by 'rndc recursing'.

bin/tests/system/statistics/clean.sh

@@ -28,4 +28,4 @@ rm -f curl.out.*
 rm -f stats*out
 rm -f ns*/managed-keys.bind*
 rm -f xsltproc.out.*
-rm -f named.stats.* ns*/named.stats.*
+rm -f named.stats.* ns*/named.stats.* ns*/named.recursing

bin/tests/system/statistics/tests.sh

@@ -98,6 +98,10 @@ getstats() {
   grep "2 recursing clients" $last_stats >/dev/null || return 1
 }
 retry_quiet 5 getstats || ret=1
+# confirm agreement with 'rndc recursing'
+$RNDCCMD -s 10.53.0.3 recursing || ret=1
+lines=$(grep -c "; client .*(tcp)" ns3/named.recursing || true)
+[ "$lines" -eq 2 ] || ret=1
 if [ $ret != 0 ]; then echo_i "failed"; fi
 status=$((status + ret))
 n=$((n + 1))