Start the merging-rebase to v2.17.1

This is the rebase to the *real* v2.17.1. Due to details of the process
that are probably pretty boring to anybody but Git for Windows'
maintainer (read: me myself), Git for Windows v2.17.1 is based on an
older revision of Git v2.17.1 that was pulled due to an influential
person who thought that .gitignore and .gitattributes should not enjoy
the same protection as .gitmodules (an assessment with which I
wholeheartedly disagree, but there's nothing I could do, my voice did
not weigh enough, I guess).

This commit starts the rebase of 8a8c948 to 5b62a68

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

Author: dscho