fix a bug in streett_to_generalized_buchi

Fixes #320.

* spot/twaalgos/totgba.cc: Fix the bug.
* NEWS: Mention the problem.
* tests/core/streett.test: Add test case.

tests/core/streett.test

@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2016, 2017 Laboratoire de Recherche et Développement
+# Copyright (C) 2016-2018 Laboratoire de Recherche et Développement
 # de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -113,3 +113,25 @@ EOF
 run 0 autcross --language-preserved \
     'autfilt --tgba %H | tee out.hoa >%O' -F streett.hoa
 grep 'generalized-Buchi 2' out.hoa
+
+
+# Issue #320
+autfilt -q --reject-word='cycle{!a;a;a;!a}' <<EOF
+HOA: v1
+States: 3
+Start: 0
+AP: 1 "a"
+acc-name: Streett 3
+Acceptance: 6 (Fin(0) | Inf(1)) & (Fin(2) | Inf(3)) & (Fin(4) | Inf(5))
+properties: trans-labels explicit-labels trans-acc deterministic
+--BODY--
+State: 0
+[!0] 0 {1 3}
+[0] 1 {}
+State: 1
+[0] 2 {2}
+State: 2
+[!0] 0 {0 4}
+[0] 2 {}
+--END--
+EOF