From: Johannes Schindelin <johannes.schindelin@gmx.de>

When specifying a merge base explicitly, there is actually no good
reason why the inputs need to be commits: that's only needed if the
merge base has to be deduced from the commit graph.

This commit is best viewed with `--color-moved
--color-moved-ws=allow-indentation-change`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Submitted-As: https://lore.kernel.org/git/pull.1647.git.1706277694231.gitgitgadget@gmail.com