PIL: write to file-compatible object fails

Binary package hint: python-imaging

>>> import io, PIL.Image
>>> img = PIL.Image.new("RGB",(10,10))
>>> stream = io.BytesIO()
>>> img.save(stream,"PPM")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/dist-packages/PIL/Image.py", line 1439, in save
    save_handler(self, fp, filename)
  File "/usr/lib/python2.6/dist-packages/PIL/PpmImagePlugin.py", line 118, in _save
    ImageFile._save(im, fp, [("raw", (0,0)+im.size, 0, (rawmode, 0, 1))])
  File "/usr/lib/python2.6/dist-packages/PIL/ImageFile.py", line 476, in _save
    fh = fp.fileno()
  File "/usr/lib/python2.6/io.py", line 480, in fileno
    self._unsupported("fileno")
  File "/usr/lib/python2.6/io.py", line 333, in _unsupported
    (self.__class__.__name__, name))
io.UnsupportedOperation: BytesIO.fileno() not supported

This is due to line 478 in ImageFile.py, where they rely on an AttributeError to be raised instead of io.UnsupportedOperation.