Pytest-New pytest names in 2.0 (flat is better than nested)

If you used older version of the py distribution (which included the
py.test command line tool and Python name space) you accessed helpers
and possibly collection classes through the py.test Python namespaces.
The new pytest Python module flaty provides the same objects,
following these renaming rules:

py.test.XYZ          -> pytest.XYZ
py.test.collect.XYZ  -> pytest.XYZ
py.test.cmdline.main -> pytest.main

The old py.test.* ways to access functionality remain valid but you
are encouraged to do global renaming according to the above rules in
your test code.