- remove ZoneTableIterator.next, is_last
- rename get_zone_table -> get_zone_table_accessor
- rename get_zones -> get_iterator
- allow get_zone_table_accessor(None) instead of "" for "any data source"
- add s_ZoneTableAccessor.base_obj to ensure in-order destruction
- get_current returns Name instead of string
- additional test cases for iterator
- general code cleanup and doc cleanup