reprepro tracking

Hi,

reprepro was accumulating lots of cruft in the pool directory. After
some investigation, it turned out that was because we had
"Tracking: all" in the reprepro config.

That means it would keep postgresql-9.1-debversion.deb around when 9.1
was out of support, and a new postgresql-debversion source was
uploaded that did not longer build the 9.1 package. It would also keep
the source for that old 9.1.deb. That's the expected part. The
unexpected part was that it was also keeping the
postgresql-10-debversion.deb package that was built from the source
that was only kept because of 9.1.deb.

I've now set it to "Tracking: minimal includebuildinfos keepsources"
which does the expected tracking.

The "includebuildinfos" part is untested, we'll see how useful that
will be.

Christoph