replace sba_explicit_* by tgba_digraph, and use tgba_digraph is postproc

This is a huge patch.  tgba_digraph are equiped with some boolean
properties that can be used to indicate whether they represent SBA
(and will carry more informations later).  All algorithms that produce
or use sba_explicit_* automata are changed to use tgba_digraph.
postproc has been rewritten using only tgba_digraph, and this required
changing the return types of many algorithms from tgba* to
tgba_digraph*.

* src/bin/dstar2tgba.cc, src/bin/ltlfilt.cc, src/dstarparse/dra2ba.cc,
src/dstarparse/dstar2tgba.cc, src/dstarparse/nra2nba.cc,
src/dstarparse/nsa2tgba.cc, src/dstarparse/public.hh,
src/tgba/tgbagraph.hh, src/tgba/tgbasafracomplement.cc,
src/tgbaalgos/compsusp.cc, src/tgbaalgos/compsusp.hh,
src/tgbaalgos/degen.cc, src/tgbaalgos/degen.hh,
src/tgbaalgos/dotty.cc, src/tgbaalgos/minimize.cc,
src/tgbaalgos/minimize.hh, src/tgbaalgos/postproc.cc,
src/tgbaalgos/postproc.hh, src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/sccinfo.cc, src/tgbaalgos/stripacc.cc,
src/tgbaalgos/stripacc.hh, src/tgbaalgos/translate.cc,
src/tgbaalgos/translate.hh, src/tgbatest/ltl2tgba.cc,
wrap/python/spot.i: Update.

src/tgba/tgbagraph.hh

@@ -411,6 +411,48 @@ namespace spot
 	}
       g_.defrag();
     }
+
+
+  protected:
+    unsigned bprops_ = 0;
+
+  public:
+    enum bprop {
+      StateBasedAcc = 1,
+      SingleAccSet = 2,
+      SBA = StateBasedAcc | SingleAccSet,
+    };
+
+    bool get_bprop(bprop p) const
+    {
+      return (bprops_ & p) == p;
+    }
+
+    void set_bprop(bprop p)
+    {
+      bprops_ |= p;
+    }
+
+    void clear_bprop(bprop p)
+    {
+      bprops_ &= ~p;
+    }
+
+    bool state_is_accepting(unsigned s) const
+    {
+      assert(get_bprop(StateBasedAcc));
+      for (auto& t: g_.out(s))
+	// Stop at the first transition, since the remaining should be
+	// labeled identically.
+	return t.acc == all_acceptance_conditions_;
+      return false;
+    }
+
+    bool state_is_accepting(const state* s) const
+    {
+      return state_is_accepting(state_number(s));
+    }
+
   };
 
 }