Testing failure on MIPS

Sorry for bombarding you with exotic failures :-)
In MIPS (little endian), the compilation of version 0.2.1 fails with
```
________________________________ test_validate _________________________________

    def test_validate():
[...]
        result = validate(get_pkg_data_filename('data/regression.xml'),
>                         output, xmllint=False)

astropy/io/votable/tests/vo_test.py:713: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

source = '/tmp/astropy-test-fOeQY2/lib.linux-mips-2.7/astropy/io/votable/tests/data/regression.xml'
output = <_io.StringIO object at 0x226f170>, xmllint = False
filename = '/tmp/astropy-test-fOeQY2/lib.linux-mips-2.7/astropy/io/votable/tests/data/regression.xml'

    def validate(source, output=sys.stdout, xmllint=False, filename=None):
[...]
        if len(lines):
            xml_lines = iterparser.xml_readlines(content_buffer)
            for warning in lines:
                w = exceptions.parse_vowarning(warning)
                if not w['is_something']:
>                   output.write(warning)
E                   TypeError: unicode argument expected, got 'str'

astropy/io/votable/table.py:242: TypeError
```
See https://buildd.debian.org/status/fetch.php?pkg=python-astropy&arch=mipsel&ver=0.2.1-1%7Eexp4&stamp=1366656559 for the full log.