For #42.

* src/graph/graph.hh, src/ltlast/multop.hh, src/ltlenv/defaultenv.hh,
src/misc/tmpfile.hh, src/tgba/taatgba.hh, src/tgba/tgbagraph.hh,
src/tgba/tgbaproduct.hh, src/tgbaalgos/gtec/gtec.hh: Declare more
classes as final.