src/tgbaalgos/tarjan_on_fly.cc,
src/tgbaalgos/nesteddfs.hh,
src/tgbaalgos/nesteddfs.cc,
src/tgbaalgos/minimalce.hh,
src/tgbaalgos/minimalce.cc,
src/tgbaalgos/colordfs.hh,
src/tgbaalgos/colordfs.cc: four new algorithms for emptyness check.

src/tgbaalgos/gtec/ce.hh,
src/tgbaalgos/gtec/ce.cc: Adapt the counter exemple for the ce
object in minimalce.hh.

src/tgbatest/ltl2tgba.cc,
src/tgbatest/emptchk.test,
src/tgbaalgos/Makefile.am: Add files for emptyness-check.


* src/tgbaalgos/reductgba_sim_del.cc: Restrict to degeneralize automata.
* src/tgba/tgbareduc.hh: src/tgba/tgbareduc.cc: Merge transition
for scc reduce.