Correct interface

The interface was not consistent. This would result in a:
```
  File "/Users/andre/work/penv/discosite/lib/python2.7/site-packages/oauthlib/oauth2/rfc6749/grant_types/authorization_code.py", line 384, in validate_token_request
    request.code, request.redirect_uri, request.client):
TypeError: confirm_redirect_uri() takes at least 6 arguments (5 given)
```