Merge remote-tracking branch 'origin/master' into rebase-to-v2.21.0

We accepted a Pull Request into `master`, but the main development
happens on the topic branch `rebase-to-v2.21.0` right now, in
preparation for the final v2.21.0 in a couple of days.

So after we forward-ported the changes in a6567c7 (Merge pull
request git-for-windows#2077 from r1walz/gzip-cmd-404, 2019-02-20), it is now time to
pull in the commit history of origin/master in a fake merge (i.e. with
`-s ours`), to make `master` fast-forward to `rebase-to-v2.21.0` again.

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

Author: dscho