fix up adnstest for r_unknown; tests for r_unknown

[adns] / regress / case-ptrbaddom.out

adns debug: using nameserver 172.18.45.6
37.45.18.172.in-addr.arpa.test.iwj.relativity.greenend.org.uk. flags 0 type 12 PTR(raw) submitted
37.45.18.172.in-addr.arpa.test.iwj.relativity.greenend.org.uk. flags 0 type 65548 PTR(checked) submitted
37.45.18.172.in-addr.arpa.test.iwj.relativity.greenend.org.uk. flags 0 type PTR(raw): OK; nrrs=1; cname=$; owner=$; ttl=60
 ptr.test.iwj.relativity.greenend.org.uk
37.45.18.172.in-addr.arpa.test.iwj.relativity.greenend.org.uk. flags 0 type PTR(checked): Domain invalid for particular DNS query type; nrrs=0; cname=$; owner=$; ttl=60
rc=0