Integrate nose with setuptools test command

Allow running the test suite via standard `python setup.py test` command as per http://nose.readthedocs.org/en/latest/setuptools_integration.html

I haven't included the changes here, but I'd also like to see tox and coverage made optional test dependencies (or more precisely, *not* tests_require). They are great for development testing, but not needed for QA testing (Eg: for OS packagers/porters)