Return error for non-IN classes in DNS server

[kchen]

The DNS server currently returns results for class IN, regardless of what class the server is queried for. For example:

kchen@scyther:~$ dig ch abra.xvm.mit.edu @sipb-xen-dev.mit.edu ;; Warning: Message parser reports malformed message packet.

; <<>> DiG 9.3.4 <<>> ch abra.xvm.mit.edu @sipb-xen-dev.mit.edu ; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4134 ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION: ;abra.xvm.mit.edu. CH A

;; ANSWER SECTION: abra.xvm.mit.edu. 900 IN A 18.181.0.105

;; AUTHORITY SECTION: xvm.mit.edu. 3600 IN SOA sipb-xen-dev.mit.edu. sipb-xen.mit.edu. 1 3600 900 3600000 21600

This doesn't operationally affect anything, of course. The server should probably return status REFUSED (which is what BIND does, except for a few special names). An NXDOMAIN response is probably OK too, since NXDOMAIN is on a per-class level, although I'm not sure what you would fill the other sections of the response with.