Note that using the ``TempFile`` module is a much cleaner way to do this. See the pynast code for examples of how to do this ([here](https://github.com/qiime/pynast/blob/master/tests/test_logger.py) is a really straight-forward example). If you have a chance to implement it here, that'd be great, but since we're not using it throughout QIIME it's not essential for this PR to be merged.