Don't store XHR requests for user redirection after log-in.

In the case that users clicked 'Log in', but the last request the server received was an XHR, they would be redirected to that XHR endpoint. This was unhelpful.

This code is called on nearly every request so I'm fielding it to see if anyone is relying on this behaviour. Will merge in a couple hours otherwise.
Sorry. My explanation was very very poorly.

I know that the `allow(request).to receive(:fullpath) { my_path }` is used in the 'before' clause because in the first spec we are expecting the my_path **is stored** in the session and in the second spec was expecting that my_path **is not stored** in the session. So, the second time the request.fullpath is not called. And if we inspecting the value of session[:return_to] on the second spec is '/anonymous?locale', so the expectation is not so clear. And when I see the code, the #store_location is private, and I don't like to test private methods directly.

So, I think it's better that we make a more real spec example on this, against a real controller **or** create a feature spec, to make sure that this behavior is working, for a normal request or a ajax request from a more real perspective.

Sorry again for bad explanation, but what do you think? I use the stub many times but Imho, there are cases that we need to test from a different perspective.