Self test fails with UnicodeDecodeError

[Andreas Gustafsson]

After fixing some other self tests by applying patches from open bug reports,
one test is still failing for me:

$ python HtmlSanitizer.py
**********************************************************************
File "HtmlSanitizer.py", line 167, in __main__.Cleaner.set_string
Failed example:
    c.string
Exception raised:
    Traceback (most recent call last):
      File "doctest.py", line 1212, in __run
        compileflags, 1) in test.globs
      File "<doctest __main__.Cleaner.set_string[2]>", line 1, in <module>
        c.string
      File "HtmlSanitizer.py", line 178, in get_string
        return unicode(self.root.renderContents())
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0: ordinal not in range(128)
**********************************************************************
1 items had failures:
   1 of 6 in __main__.Cleaner.set_string
***Test Failed*** 1 failures.