initial implementation of filter-aaaa.so as a shared object

initial implementation of filter-aaaa.so as a shared object

- temporary kluge! in this version, for testing purposes,
  named always searches for a filter-aaaa module at /tmp/filter-aaaa.so.
  this enables the filter-aaaa system test to run even though the
  code to configure hooks in named.conf hasn't been written yet.
- filter-aaaa-on-v4, filter-aaaa-on-v6 and the filter-aaaa ACL are
  still configured in the view as they were before, not in the hook.