* src/tgba/tgbagraph.cc: New file.
* src/tgba/Makefile.am: Adjust.
* src/tgba/tgbagraph.hh (set_single_acceptance_set,
new_acc_transition): New methods.
(set_acceptance_conditions, merge_transitions): Move body
to tgbagraph.cc.
* src/tgbaalgos/complete.cc, src/tgbaalgos/degen.cc,
src/tgbaalgos/dtbasat.cc, src/tgbaalgos/dtgbacomp.cc,
src/neverparse/neverclaimparse.yy, src/dstarparse/dra2ba.cc,
src/dstarparse/nra2nba.cc: Simplify using these new methods.