add support for re-authentication

as discussed here, https://github.com/facebook/facebook-php-sdk-v4/pull/309

adds a new base method to generate url : makeUrl()
and other  3 methods to get a login URL, re-request URL & re-authentication URL. 
Since all the URL-generating methods require `$redirectUrl`, that should be handled by this method.

And `$scope` should also be handled in this method for the same reason.

So `getReRequestUrl()` and `getReAuthenticationUrl()` would just be adding the proper `auth_type` param to the `$params` array and passing the rest of the args to `makeUrl()`.

So the header would look like this:

```php
private function makeUrl($redirectUrl, array $scope, array $params, $version, $separator)
```