Some methods cause an OAuth error

Some Flickr methods cause an OAuth error:

```
Flickr::OAuthError: Signature invalid
```

So far Flickr methods which are known to cause this error are:
- `flickr.photos.transform.rotate`
- `flickr.photosets.reorderPhotos`

It is not a bug with Flickr, because it works when using the `flickraw` gem. Perhaps it's a bug with the `simple_oauth` gem, which I have no clue how to debug.
