Change readshort() to work with unsigned values
Add support for using an unspecified RR type

Add PRIVATE query type with id 65399 (private use range).
According to RFC3597 the reply data in a query with unspecified RR type must be handled
as unstructured binary data, which means it can contain raw packet data just like the NULL type.
Since the reply format is optimal it is ordered just after NULL in the priority order.