'WSGIRequest' object has no attribute 'host'

In la_facebook.callbacks.base.BaseFacebookCallback.redirect_url there is a 'safety' check:

``if netloc and netloc != request.host:``

This breaks as the request object has no attribute by this name. I've updated this to use the pattern preferred by the [Django documentation](https://docs.djangoproject.com/en/1.3/ref/request-response/#django.http.HttpRequest.get_host) (i.e., request.get_host()).