Start the merging-rebase to 7dcd3d8

In preparation for v2.22.0-rc0, we rearrange quite a few topics in this
branch thicket.

Apart from a reworded comment, this does not introduce any new change.

This commit starts the rebase of 7dcd3d8 to 7dcd3d8

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

Author: dscho