Temporarily restore the bundled six to avoid breaking dependant libraries.

theano/tests/test_flake8.py

@@ -19,6 +19,7 @@ __copyright__ = "(c) 2015, Universite de Montreal"
 __contact__ = "Saizheng Zhang <saizhenglisa..at..gmail.com>"
 
 whitelist_flake8 = [
+    "compat/six.py",  # This is bundled code that will be deleted, don't fix it
     "__init__.py",
     "tests/test_gradient.py",
     "tests/test_config.py",