pywatchman: make tests compatible with Python 2.6
pywatchman: make tests compatible with Python 2.6

Python 2.6 doesn't support the `with self.assertRaises` form.

dhruvsinghal/watchman,facebook/watchman,kwlzn/watchman,dhruvsinghal/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,facebook/watchman,dhruvsinghal/watchman,facebook/watchman,dhruvsinghal/watchman,nodakai/watchman,nodakai/watchman,dhruvsinghal/watchman,kwlzn/watchman,kwlzn/watchman,kwlzn/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,nodakai/watchman,dhruvsinghal/watchman,kwlzn/watchman,facebook/watchman,nodakai/watchman,wez/watchman,facebook/watchman,nodakai/watchman,dhruvsinghal/watchman,kwlzn/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,kwlzn/watchman,wez/watchman,dhruvsinghal/watchman,wez/watchman,facebook/watchman,facebook/watchman