threading.Event is a class for python 3.3+ but not for python 3.2

Python has changed the trheading module between python 3.2 and 3.3. Unfortunatly, due to a doc bug, it appears as threading.Thread is a class, but it really isn't.

See trace: https://travis-ci.org/getsentry/raven-python/jobs/6748191

3.2 function:
http://docs.python.org/3.2/library/threading.html
threading.Event()
A factory function that returns a new event object.

3.3 class:
http://docs.python.org/3.3/library/threading.html#threading.Thread