implement conversion to GRA and GSA

Fixes #174.

* spot/twaalgos/totgba.hh, spot/twaalgos/totgba.cc
(to_generalized_streett, to_generalized_rabin): New functions.
* spot/twa/acc.hh: Declare more methods as static.
* bin/autfilt.cc: Implement --generalized-rabin and
--generalized-streett options.
* NEWS: Mention these.
* tests/core/gragsa.test: New file.
* tests/Makefile.am: Add it.

tests/Makefile.am

@@ -207,6 +207,7 @@ TESTS_twa = \
   core/complete.test \
   core/complement.test \
   core/remfin.test \
+  core/gragsa.test \
   core/dstar.test \
   core/readsave.test \
   core/ltldo.test \

tests/core/gragsa.test

@@ -0,0 +1,31 @@
+#!/bin/sh
+# -*- coding: utf-8 -*-
+# Copyright (C) 2016 Laboratoire de Recherche
+# et Développement de l'Epita (LRDE).
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# Spot is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. ./defs
+set -e
+
+randltl -n 100 p1 p2 p3 --tree-size 5..15 --seed=200 |
+ltlcross --timeout=60 \
+"ltl2tgba %f > %T" \
+"ltl2tgba -G -D %f > %T" \
+"ltl2tgba -G -D %f | autfilt --gsa=unique-fin > %T" \
+"ltl2tgba -G -D %f | autfilt --gra=unique-inf > %T" \
+"ltl2tgba -G -D %f | autfilt --gsa=share-fin > %T" \
+"ltl2tgba -G -D %f | autfilt --gra=share-inf > %T"