Missing argument in services.yml doesn't keep track of factory methods

The missing argument inspection in services definition doesn't understand if the service is created by a factory. Example:

``` yml
services:
  service:
    class: MyClass
    factory_class: MyClass
    factory_method: factory      
```

``` php
class MyClass
{
    public function __construct($a, $b) {}

    public function factory() {}
}
```

I believe this was added in last update?
