* Must always be non-null pointer;
* If *query_io is 0 to start with then any query may be returned;
* If *query_io is !0 adns_query then only that query may be returned.
* Must always be non-null pointer;
* If *query_io is 0 to start with then any query may be returned;
* If *query_io is !0 adns_query then only that query may be returned.