Start the merging-rebase to v2.39.1-2-g37537d6472d8

The intention is to re-arrange Git for Windows' branch thicket a bit (so
that the merge of the `readme` branch is the tip again), and to rebase
on top of the fixes that Git for Windows included in v2.39.1 which were
cherry-picked into Git's `maint` branch.

This commit starts the rebase of 5501b4a to 37537d6

Author: dscho