[schema] Make syntax compatible with print_function
yams seems to exec() us sometimes (instead of __import__()), and
yams.reader uses print_function nowadays.
for table, column in [
('transactions', 'tx_time'),
('tx_entity_actions', 'tx_uuid'),
('tx_relation_actions', 'tx_uuid')]:
repo.system_source.create_index(session, table, column)
commit()