[5.0] Redirect User to Intended Url After Login

Redirect the logged in user to the intended URL if one exists instead of forcing her to go to the defined redirect path.

This nicely complements the `redirect()->guest('auth/login')` in the [Authenticate middleware](https://github.com/laravel/laravel/blob/develop/app/Http/Middleware/Authenticate.php#L44).
Merge pull request #6622 from miclf/patch-3

[5.0] Redirect User to Intended Url After Login