Currently ginac misses vcs fields in debian/control, and upstream (you ;-)) for
some reason does not carry (or just does not expose) Debian packaging
within

http://www.ginac.de/ginac.git

So, why not to expose debian/ branch (or some other branch) within upstream git
repository, and (optionally) provide debian/gbp.conf listing what is the branch
with debian packaging and what is upstream, so people could just debcheckout
ginac and git-buildpackage it ;) ?

Availability of vcs fields would make it easier to contribute patches to
packaging or upstream.

Cheers,
Yarik