tsb diff

It would be really nice for tsb to be able to provide a "metadiff" of all the changesets between builds. This would take two changesets that belong to the tsb repo and diff the contents of the repo, then taking that diff, determining how that affects the sourced repos and producing a list of changesets that were added or removed.

This isn't really a small feature, but it's an important one.

The issue names no files, tests, or entry points. Start by locating how tsb records changesets, compares builds, and tracks sourced repositories; define the metadiff inputs, repository traversal, and expected added or removed changeset output before implementation.

Written by the indexing model from the issue text.