Change use of ascii to broad utf-8

#### Bug

when calling the `put_photo` method with non ascii char in the message (french, spanish or russian message) this broke.

ex:
```
message = u'été à Paris'
api = facebook.GraphAPI(access_token)
api.put_photo(image, message, album_id)
```

leads to a `UnicodeEncodeError: 'ascii' codec can't encode character ...`

#### to test

try the above code with a valid access_token/album_id/image