Comment 4 for bug 1505742

The code for this is BuildManager.choose_packages() at:

http://bazaar.launchpad.net/~cupstream2distro-maintainers/cupstream2distro/trunk/view/head:/citrain/build.py#L77

It would need to iterate on self.silo_state.mps and automatically include things that are found to have new commits/new MPs.