The upstream Git repo is on GitHub and can be added as an additional
git remote add upstream-repo https://github.com/JabRef/jabref.git
This allows to use gbp-import-orig's --upstream-vcs-tag option.
The repo at https://github.com/koppor/jabref.git also has a debian branch
which is used to create some of the debian/patches.
The 3.8.1 source tarball was prepared using uscan, which removes the
./lib/ and ./gradle/ directories, plus MacAdapter.java, since they are
excluded in debian/copyright.
Patch 001_koppor_debian_3.8.1.patch was prepared by generating the
git diff of upstream tag v3.8.1 and Oliver Kopp's curated 3.8.1 debian