Fixed a test to correctly calculate a fixture's relative path.

    # fixtures_regress depending on how runtests.py is invoked.

    # All path separators must be / in order to be a proper regression test on

    # Windows, so replace as appropriate.

    relative_prefix = current_dir.replace(os.getcwd(), '', 1)[1:].replace('\\', '/')

    relative_prefix = os.path.relpath(current_dir, os.getcwd()).replace('\\', '/')

    fixtures = [relative_prefix + '/fixtures/absolute.json']

    def test_fixtures_loaded(self):