obslog: also display patch for rebased changesets This applies the same logic that is used for "merge-diff" to rebased changesets. The successors' content is compared to the content of the predecessors rebased in-memory on the new parents. This highlights the changes that were actually introduced while rebasing (like conflict resolution or API adjustment). As a side effect, obslog now also outputs slightly more diffs for splits, showing what parts of the original big changeset were moved to the smaller split components (but for now it only works for the first few changesets).