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, leading
for the final v2.21.0 tag that was *just* published.

Since we just forward-ported the changes in c86d193 (Merge pull
request #2088 from dscho/test-oid-fix-windows, 2019-02-24), we can
safely 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 <johannes.schindelin@gmx.de>

Author: dscho