re-introduce relative imports to unbork python 3.

test/test_freeze.py

@@ -12,7 +12,7 @@ from dataset import connect
 from dataset.freeze.app import freeze
 from dataset.freeze.format.fcsv import value_to_str
 
-from sample_data import TEST_DATA
+from .sample_data import TEST_DATA
 
 
 class FreezeTestCase(unittest.TestCase):

test/test_freeze_app.py

@@ -14,7 +14,7 @@ from dataset import connect
 from dataset.util import FreezeException
 from dataset.freeze.config import Configuration, Export
 from dataset.freeze.app import create_parser, freeze_with_config, freeze_export
-from sample_data import TEST_DATA
+from .sample_data import TEST_DATA
 
 
 class FreezeAppTestCase(unittest.TestCase):

test/test_persistence.py

@@ -12,7 +12,7 @@ from sqlalchemy.exc import IntegrityError, SQLAlchemyError
 from dataset import connect
 from dataset.util import DatasetException
 
-from sample_data import TEST_DATA, TEST_CITY_1
+from .sample_data import TEST_DATA, TEST_CITY_1
 
 
 class DatabaseTestCase(unittest.TestCase):