Fix #2207

@Lukasa wrote the fix in #2207 

With this, the expected behaviour is restored (a `TooManyRedirects` error);

```pycon
>>> import requests
r>>> r = requests.get('http://www.dx.com/p/-268479')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "./requests/api.py", line 59, in get
    return request('get', url, **kwargs)
  File "./requests/api.py", line 48, in request
    return session.request(method=method, url=url, **kwargs)
  File "./requests/sessions.py", line 451, in request
    resp = self.send(prep, **send_kwargs)
  File "./requests/sessions.py", line 583, in send
    history = [resp for resp in gen] if allow_redirects else []
  File "./requests/sessions.py", line 583, in <listcomp>
    history = [resp for resp in gen] if allow_redirects else []
  File "./requests/sessions.py", line 111, in resolve_redirects
    raise TooManyRedirects('Exceeded %s redirects.' % self.max_redirects)
requests.exceptions.TooManyRedirects: Exceeded 30 redirects.
```