This trick was performed by rebasing the builtin-stash-rebase-v2 branch
thicket via `git rebase -ki --rebase-merges=rebase-cousins v2.19.1`,
replacing all branches that made it into `pu` by their current versions
(and also the builtin-stash by the newest iteration as of ungps/git),
labeling the branch as `builtin-stash-rebase-v3` and then replacing it
in the `merge` command in the todo list.
We did have to rebase the "cousins" because the initial merge of a
merging-rebase will confuse the merge-base logic (and hence the changes
would be dropped when we try to merge them "again").
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
18a869b96b