Add more detail to exception text

Add query/type to exception text, so it is easier to find the cause.
Only add extra query if necessary

If there have been previous queries made for a given name, then don't
query.
Don't query TXT twice

If name has _domainkey and is also a zone, then TXT might be potentially
be called twice, so perform a check to make sure it's not.
Don't look for CNAME chaing with DLV domain