Quick fix for breaking change in Laravel 4

A recent laravel-4 update made the method Input::hasSessionStore() deprecated; breaking validation. The method to be used instead is Input::hasSession().

The current master throws this exception:
```
PHP Fatal error: Call to undefined method Illuminate\Http\Request::hasSessionStore() in vendor/laravel/framework/src/Illuminate/Support/Facades/Facade.php on line 205
```

This change fixes it. See issue #155