Use more flexible "Consumer extends" for list of step instances.

In my project i want to pass a List of InjectableStep (which is a marker interface).
But i cannot pass my List<? super InjectableStep> or even List<InjectableStep> to the constructor of InstanceStepsFactory.

See http://stackoverflow.com/a/252860/1325574 for further details of the "Producer Extends Consumer Super" idea.