* src/taalgos/minimize.hh, src/taalgos/minimize.cc: implements a
minimization of TA by merging bisimular states.
* src/taalgos/statessetbuilder.hh, src/taalgos/statessetbuilder.cc:
returns the set of reachable states of a TA (used in minimize.cc).
* src/taalgos/Makefile.am: add them.
* src/tgbatest/ltl2tgba.cc: add commands to test TA minimization