- the purpose of this change is allow for more well-defined hook points
  to be available in the query processing logic. some functions that
  formerly didn't have access to 'qctx' do now; this is needed because
  'qctx' is what gets passed when calling a hook function.
- query_addrdataset() has been broken up into three separate functions
  since it used to do three unrelated things, and what was formerly
  query_addadditional() has been renamed query_additional_cb() for
  clarity.
- client->filter_aaaa is now qctx->filter_aaaa. (later, it will be moved
  into opaque storage in the qctx, for use by the filter-aaaa module.)
- cleaned up style and braces