setup.py: Loosen the pyVows dependency to blacklist bad versions

1d264b96 (Pyvows 2.0.5 has broken tornado_pyvows, 2014-05-19)
mentioned pyVows 2.0.5, but also blocked 2.0.4.  Since then, there has
been a 2.0.6 release which tried to fix this issue 59e67374 (topics
can be none, we need to validate against that, 2014-06-02, [1]) but
failed [2].  Instead of ignoring all future pyVows development, only
blacklist the versions we know to be broken.

[1]: https://github.com/heynemann/pyvows/commit/59e67374bcfbf7c8c45a4be575e8eae64902c209
[2]: https://github.com/heynemann/pyvows/pull/115
     Summary: runner.gevent: Shift None check for topic_func earlier
     Date: 2014-10-08