setup stdout prior to test setup. Fixes #7

Previously ``self._stdout`` was only set prior to the running of the test itself but not the setup method. Any errors in setup would throw an ``AttributeError``  when the test runner called  PipedTestResult.addError. 

This PR adds  _setupStdout and _restoreStdout  methods which are called  in ``TestResult.startTest`` and ``TestResult.stopTest`` 

Fixes #7.