Except for tests that include non-unicode characters:
tests/test_po.py
tests/test_strformat.py
tests/test_url.py
tests/checker/test_error.py
tests/checker/test_news.py
MS Word files are binary data, and get_temp_filename() will write them
to disk using open(..., 'wb'), so we want to pass bytes in there, not
Unicode.
See #323.