Time not frozen if TestCase has a setUp method that does not call super()

Since `unittest.TestCase.setUp` is a stub function, it's extremely common for subclasses' `setUp` methods to not call `super()`.  This translates to time not being frozen for these subclasses when decorated.  Also, worryingly, if a custom `setUp` called `super()`, but a custom `tearDown` didn't... time would probably be frozen for the remainder of the test run!

A more reliable method, in my experience, is passing the decoration on to the TestCase subclass's `run` method.  This works because unittest tests are run by instantiating the TestCase subclass with the name of the test method to run, and then calling its `run` method.