Possible bug report: imagehash.average_hash throws an exception on image resize.

Hi,

In the find_similar_images.py example when running on a large set of images I encountered a problem.
Sometimes average_hash throws an exception (Mac OS X 10.9 Python2.7):
```python
    hash = hashfunc(Image.open(path))
  File "/Library/Python/2.7/site-packages/imagehash/__init__.py", line 97, in average_hash
    image = image.convert("L").resize((hash_size, hash_size), Image.ANTIALIAS)
  File "/Library/Python/2.7/site-packages/PIL/Image.py", line 710, in convert
    self.load()
  File "/Library/Python/2.7/site-packages/PIL/ImageFile.py", line 218, in load
    raise IOError("image file is truncated (%d bytes not processed)" % len(b))
```

This is similar to http://stackoverflow.com/questions/12984426/python-pil-ioerror-image-file-truncated-with-big-images and might be a result of aspect ratio problem?
I haven't dug deeply enought into the code to understand what is the cause of this.

Thanks!