[BrowserKit] Fixed the handling of parameters when redirecting

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This fixes the handling of request parameters after 2d34e78aafa0e170845a23d0e163b3a15569fa8e to avoid sending POST parameters as GET parameters in the next request.

In case of a 307 redirect on a GET request, I'm not sure of the expected behavior. Should we re-add the GET parameters in the URI ? I would make things inconsistent between ``$client->request('GET', 'http://www.example.com/?foo=bar')`` and ``$client->request('GET', 'http://www.example.com/', array('foo' => 'bar')``