postproc: simplify the acceptance condition

* spot/twaalgos/postproc.cc: Here.
* spot/twaalgos/cobuchi.cc, spot/twaalgos/totgba.cc: Fix some bug
uncovered by the new simplified automata.
* tests/core/satmin2.test, tests/core/sccdot.test,
tests/core/sim3.test, tests/python/decompose.ipynb,
tests/python/satmin.ipynb: Update expected results.
* NEWS: Mention the simplification and the bug.

tests/core/satmin2.test

@@ -335,7 +335,8 @@ HOA: v1
 States: 1
 Start: 0
 AP: 1 "a"
-Acceptance: 2 (Inf(0) & Fin(1)) | (Fin(0) & Inf(1))
+acc-name: generalized-co-Buchi 2
+Acceptance: 2 Fin(0)|Fin(1)
 properties: trans-labels explicit-labels trans-acc colored complete
 properties: deterministic
 --BODY--

tests/core/sccdot.test

@@ -156,7 +156,7 @@ HOA: v1
 States: 8
 Start: 0
 AP: 2 "a" "b"
-Acceptance: 3 (Inf(0)&Inf(1)) & Fin(2)
+Acceptance: 3 Fin(2) & (Inf(0)&Inf(1))
 properties: trans-labels explicit-labels trans-acc
 --BODY--
 State: 0

tests/core/sim3.test

@@ -1,7 +1,7 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2015 Laboratoire de Recherche et Développement de
-# l'Epita (LRDE).
+# Copyright (C) 2015, 2018 Laboratoire de Recherche et Développement
+# de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
 #
@@ -55,25 +55,25 @@ HOA: v1
 States: 5
 Start: 0
 AP: 2 "b" "a"
-acc-name: Rabin 2
-Acceptance: 4 (Fin(0) & Inf(1)) | (Fin(2) & Inf(3))
+acc-name: Streett 1
+Acceptance: 2 Fin(0) | Inf(1)
 properties: trans-labels explicit-labels state-acc complete
 properties: deterministic
 --BODY--
 State: 0
 [!1] 1
 [1] 3
-State: 1 {1 3}
+State: 1 {1}
 [0&!1] 1
 [!0&!1] 2
 [0&1] 3
 [!0&1] 4
-State: 2 {1}
+State: 2
 [0&!1] 1
 [!0&!1] 2
 [0&1] 3
 [!0&1] 4
-State: 3 {0 3}
+State: 3 {0 1}
 [0&!1] 1
 [!0&!1] 2
 [0&1] 3