* Only create one build commit which contains multiple artifact trees,
rather than one per artifact. This is atomic. We can use the new
compose syntax like foo:/devel to slice out the /devel tree.
* Create the minimal buildroot for each component by composing the
previous components in the build order, instead of continually
updating one big tree.
* Ensure the artifact builder gets empty directories in /etc
The collection of Python scripts here have gotten to the point where
we need to share code. Start refactoring things so that we have one
main command which imports subcommands as libraries.
Colin Walters