- [bug] A significant change to how labeling

- [bug] A significant change to how labeling
is applied to columns in SELECT statements
allows "truncated" labels, that is label names
that are generated in Python which exceed
the maximum identifier length (note this is
configurable via label_length on create_engine()),
to be properly referenced when rendered inside
of a subquery, as well as to be present
in a result set row using their original
in-Python names.   [ticket:2396]

- apply pep8 to test_labels