Update testing basics doc and add helper tool to run tests without warnings

In Python 2.7.6, deprecation warnings were quieted by default. In Django 1.5, deprecation warnings are passed to the console by default overiding Python's default behavior. It would be nice to explain to the user how to run the tests without deprecation warnings.

A section has been added to the testing basics documentation page. 

A simple helper tool to run test suite without warnings has been added as a convenience for developers.
I'd put deprecation warnings in quotes rather than capitalize, but that seems even more nitpicky than usual.