Artifact downloader should support downloading artifacts from triggering plan.

We have a number of plans that all require the same post-processing/deployment step (with a few variable items that are defined as variables/etc. on the plan).

It would be very nice to be able to have a single dependency plan that handles that work for every such plan. However the post-processing/deployment step needs shared artifacts from the triggering plan and, as far as I can tell, there isn't a way to have the Artifact Download task use the triggering plan as its source.

I realize the difficulty in supporting downloading specific artifacts from different triggering plans if they have different artifacts but even only supporting all artifacts would be useful (and supporting a manually specified artifact name and accepting build failures if that doesn't exist would be even better).