* src/tgbaalgos/degen.cc, src/tgbaalgos/degen.hh: New files, with
most of the logic extracted from src/tgba/tgbatba.cc (SBA version).
* src/tgbaalgos/Makefile.am: Distribute these.
* src/tgbatest/ltl2tgba.cc: Use the new degeneralization instead of
the on-the-fly version.