Weird, I could swear that I only did debian/rules binary (or equivalent) followed by make distclean. But it must have been removed by debian/rules clean nevertheless. No big deal, I think, since we build --without-java.
Anyway, I've replaced the contents of the very messy clean target with just a $(MAKE) distclean (actually it just deletes the build directory), and it seems to be sufficient, except for one thing: The official tarballs don't contain the built documentation, which Marek's tarballs, built from CVS, did, so $(MAKE) documentation is needed, but there doesn't seem to be any corresponding clean-documentation target (make -C refdoc spotless doesn't work, because refdoc/.cvsigore is not in the tarball). However, I think rm refdoc/modref refdoc/traditional_manual does it.