sccinfo: adjust to work with alternating automata

* spot/twaalgos/sccinfo.cc: Consider universal edges as if they were
existential edges.
* spot/twaalgos/sccinfo.hh: Document that.
* spot/twaalgos/dot.cc: Allow option 's' again, for easy testing.
* tests/core/alternating.test: Adjust tests.
* tests/python/_altscc.ipynb: New file (more tests).
* tests/Makefile.am: Add it.

tests/core/alternating.test

@@ -53,7 +53,6 @@ State: 6 "t"
 --END--
 EOF
 
-# The 's' option should be ignored for alternating automata
 autfilt --dot=bans alt.hoa >alt.dot
 
 cat >expect.dot <<EOF
@@ -66,7 +65,41 @@ digraph G {
     -11 [label=<>,width=0,height=0,shape=none]
     -11 -> 0
     -11 -> 2
+  subgraph cluster_0 {
+  color=green
+  label=""
+  6 [label="t"]
+  }
+  subgraph cluster_1 {
+  color=red
+  label=""
+  4 [label="F(b)\n⓿"]
+  }
+  subgraph cluster_2 {
+  color=green
+  label=""
+  3 [label="GF(b)"]
+  }
+  subgraph cluster_3 {
+  color=green
+  label=""
+  2 [label="G(a)"]
+  }
+  subgraph cluster_4 {
+  color=red
+  label=""
+  1 [label="FG(a)\n⓿"]
+  }
+  subgraph cluster_5 {
+  color=red
+  label=""
+  5 [label="((a) U (b))\n⓿"]
+  }
+  subgraph cluster_6 {
+  color=black
+  label=""
   0 [label="((((a) U (b)) && GF(b)) && FG(a))"]
+  }
   0 -> -1 [label="b", dir=none]
     -1 [label=<>,width=0,height=0,shape=none]
     -1 -> 3
@@ -76,24 +109,18 @@ digraph G {
     -4 -> 5 [style=bold, color="#F15854"]
     -4 -> 3 [style=bold, color="#F15854"]
     -4 -> 1 [style=bold, color="#F15854"]
-  1 [label="FG(a)\n⓿"]
   1 -> 2 [label="a"]
   1 -> 1 [label="1"]
-  2 [label="G(a)"]
   2 -> 2 [label="a"]
-  3 [label="GF(b)"]
   3 -> 3 [label="b"]
   3 -> -8 [label="!b", style=bold, color="#FAA43A", dir=none]
     -8 [label=<>,width=0,height=0,shape=none]
     -8 -> 4 [style=bold, color="#FAA43A"]
     -8 -> 3 [style=bold, color="#FAA43A"]
-  4 [label="F(b)\n⓿"]
   4 -> 6 [label="b"]
   4 -> 4 [label="!b"]
-  5 [label="((a) U (b))\n⓿"]
   5 -> 6 [label="b"]
   5 -> 5 [label="a & !b"]
-  6 [label="t"]
   6 -> 6 [label="1"]
 }
 EOF