Code review comment for lp://staging/~coreygoldberg/window-mocker/py3

Note that io.StringIO insists on writing unicode objects only, so it does behave differently than StringIO.StringIO in Python 2.7. If window-mocker carefully converts everythign that's fine, but doing so will break the Python 3 support. So far I must say I avoid io.StringIO in code that supports both py 2 and 3 as it makes the code quite ugly (lots of "if sys.version" checks). But YMMV.