Indirect lookup via another IComponentKey

Use this in e.g. binding.Obtain to look up something indirectly, like:

        class MyClass(binding.Component):

            socketURL = "fd:0"

            socket = binding.Obtain(
                naming.Indirect('socketURL'), adaptTo=[IListeningSocket]
            )

Instances of the above class will have a socket attribute that is the result of looking up the URL provided by the instance's socketURL attribute at runtime.

__init__ (
        self,
        key,
        default=NOT_GIVEN,
        )

findComponent (
        self,
        component,
        default=NOT_GIVEN,
        )