streett_to_generalized_buchi: fix incorrect algorithm

Fixes #284, reported by Juraj Major.

* spot/twaalgos/totgba.cc: Fix the algorithm.
* spot/twa/acc.hh: More doc for future generations.
* tests/core/scc.test: More test cases.
* NEWS: Mention the issues.

tests/core/scc.test

@@ -139,3 +139,56 @@ State: 3 {1}
 --END--
 EOF
 test 2 = `autfilt --stats=%[a]c in.hoa`
+
+# From issue #284, reported by Juraj Major.
+cat >in.hoa <<EOF
+HOA: v1
+States: 4
+Start: 0
+AP: 1 "a"
+Acceptance: 8 Fin(5) & Fin(3) & (Inf(6) | Fin(7)) &
+              (Inf(2) | Fin(1)) & (Inf(4) | Fin(0))
+properties: trans-labels explicit-labels trans-acc complete
+spot.highlight.edges: 3 5 11 5 14 5
+--BODY--
+State: 0
+[t] 0 {0}
+[0] 1 {4}
+[!0] 2 {4}
+[0] 0 {2 3}
+[!0] 0 {1}
+State: 1
+[!0] 1 {0}
+[!0] 3 {4}
+[!0] 1 {1}
+[0] 1 {4 5}
+[0] 1 {2 3 5}
+State: 2
+[0] 2 {0 6}
+[0] 3 {4 6}
+[0] 2 {2 3 6}
+[!0] 2 {4 7}
+State: 3
+[0] 3 {4 5 6}
+[0] 3 {2 3 5 6}
+[!0] 3 {4 7}
+--END--
+/* this variant also cause some issues while fixing the above */
+HOA: v1
+States: 1
+Start: 0
+AP: 1 "a"
+Acceptance: 5 Fin(0) & (Inf(1) | Fin(2)) & (Inf(4))
+--BODY--
+State: 0
+[0] 0 {1}
+[0] 0 {0 1}
+[!0] 0 {4 2}
+--END--
+EOF
+autfilt --stats='%[a]c' in.hoa >out
+cat >exp <<EOF
+1
+1
+EOF
+diff out exp