Start the merging-rebase to v2.14.0-rc1

As v2.14.0 (final) is less than two weeks away, and as the most recent
"What's Cooking" mail has not indicated any maintenance release anytime
soon, let's prepare for v2.14.0 already now by rebasing onto v2.14.0-rc1,
so that https://wingit.blob.core.windows.net/files/index.html gets an
early preview.

A couple of patches had to be adjusted because the code changed in core
Git while the patches are still in flight.

While at it, the rebase-i-extra patch series has been updated to the most
recent iteration.

This commit starts the rebase of 0709ae1 to 418951619bc

Signed-off-by: Johannes Schindelin <[email protected]>