Modify the ELTL parser to be able to support PSL operators. Add a

new keyword in the ELTL format: finish, which applies to an
automaton operator and tells whether it just completed.

* src/eltlparse/eltlparse.yy: Clean it. Add finish.
* src/eltlparse/eltlscan.ll: Add finish.
* src/formula_tree.cc, src/formula_tree.hh: New files. Define a
small AST representing formulae where atomic props are unknown
which is used in the ELTL parser.
* src/ltlast/automatop.cc, ltlast/automatop.hh, ltlast/nfa.cc,
ltlast/nfa.hh: Adjust.
* src/ltlast/unop.cc, src/ltlast/unop.hh: Finish is an unop.
* src/ltlvisit/basicreduce.cc, src/ltlvisit/nenoform.cc,
src/ltlvisit/reduce.cc, src/ltlvisit/syntimpl.cc,
src/ltlvisit/tostring.cc, src/ltlvisit/tunabbrev.cc,
src/tgba/formula2bdd.cc, src/tgbaalgos/ltl2tgba_fm.cc,
src/tgbaalgos/ltl2tgba_lacim.cc: Handle finish in switches.
* src/tgbaalgos/eltl2tgba_lacim.cc: Translate finish.
* src/tgbatest/eltl2tgba.test: More tests.

src/ltlvisit/basicreduce.cc

@@ -223,6 +223,10 @@ namespace spot
 
 	      result_ = unop::instance(unop::G, result_);
 	      return;
+
+	    case unop::Finish:
+	      result_ = unop::instance(unop::Finish, result_);
+	      return;
 	    }
 	  /* Unreachable code.  */
 	  assert(0);

src/ltlvisit/nenoform.cc

@@ -102,6 +102,12 @@ namespace spot
 	      result_ = unop::instance(negated_ ? unop::F : unop::G,
 				       recurse(f));
 	      return;
+
+	    case unop::Finish:
+	      result_ = unop::instance(unop::Finish, recurse_(f, false));
+	      if (negated_)
+		result_ = unop::instance(unop::Not, result_);
+	      return;
 	    }
 	  /* Unreachable code.  */
 	  assert(0);

src/ltlvisit/reduce.cc

@@ -97,6 +97,10 @@ namespace spot
 		  || !is_universal(result_))
 		result_ = unop::instance(unop::G, result_);
 	      return;
+
+	    case unop::Finish:
+	      result_ = unop::instance(unop::Finish, result_);
+	      return;
 	    }
 	  /* Unreachable code.  */
 	  assert(0);

src/ltlvisit/syntimpl.cc

@@ -241,6 +241,8 @@ namespace spot
 	      if (syntactic_implication(f, constant::false_instance()))
 		result_ = true;
 	      return;
+	    case unop::Finish:
+	      return;
 	    }
 	  /* Unreachable code.  */
 	  assert(0);
@@ -431,6 +433,8 @@ namespace spot
 		destroy(tmp);
 		return;
 	      }
+	    case unop::Finish:
+	      return;
 	    }
 	  /* Unreachable code.  */
 	  assert(0);

src/ltlvisit/tostring.cc

@@ -144,6 +144,10 @@ namespace spot
 	    case unop::G:
 	      os_ << "G";
 	      break;
+	    case unop::Finish:
+	      os_ << "finish";
+	      need_parent = true;
+	      break;
 	    }
 
 	  top_level_ = false;
@@ -297,6 +301,10 @@ namespace spot
 	    case unop::G:
 	      os_ << "[]";
 	      break;
+	    case unop::Finish:
+	      os_ << "finish";
+	      need_parent = true;
+	      break;
 	    }
 
 	  top_level_ = false;

src/ltlvisit/tunabbrev.cc

@@ -39,6 +39,7 @@ namespace spot
     {
       switch (uo->op())
 	{
+	case unop::Finish:
 	case unop::X:
 	case unop::Not:
 	  this->super::visit(uo);