formula automaton and the synchronized product) from LBTT.
Idea from Jean-Michel Couvreur.

* src/tgbaalgos/lbtt.cc (nonacceptant_lbtt_bfs): New class.
(nonacceptant_lbtt_reachable): New function.
* src/tgbaalgos/lbtt.hh (nonacceptant_lbtt_reachable): New
function.
* src/tgbatest/ltl2tgba.cc (main): Call nonacceptant_lbtt_reachable
if the -T option is used.
* src/tgbatest/spotlbtt.test: Setup the -T variants, disabled by
default.