Local backflow doesn't operate like the VMR backflow

[mmitche]

It should, in almost all cases, be possible mimic the behavior of the service with local darc commands. It is common to run these locally to combine various sorts of updates together, or debug issues, etc.

I would expect that darc vmr backflow would have modes that would enable it to operate like the service. Update based on a build id, so that my local repo gets updated with the source changes + dependencies of the VMR build. It looks like it only operates over source changes though.

I suggest one of two approaches:

• Integrate build info knowledge into vmr forward/backflow.
• Integrate VMR knowledge into update-dependencies