autfilt: Better display of cluster when universal edge loops in it

Fixes #208

* NEWS: Informations about the modifications
* spot/twaalgos/dot.cc (print): Gestion of cluster for
universal transitions
* tests/core/alternating.test: tests added
* tests/core/neverclaimread.test: tests changed for
new dot format
* tests/core/readsave.test: tests changed
* tests/core/sccdot.test: tests changed
* tests/python/_altscc.ipynb: tests changed
* tests/python/decompose.ipynb: tests changed

tests/core/readsave.test

@@ -327,21 +327,21 @@ digraph G {
   subgraph cluster_0 {
   color=green
   1 [label="s1", peripheries=2]
+  1 -> 1 [label="a"]
   }
   subgraph cluster_1 {
   color=green
   0 [label="s0", peripheries=2]
+  0 -> 0 [label="b"]
   }
   subgraph cluster_2 {
   color=black
   3 [label="s3"]
-  }
-  0 -> 0 [label="b"]
-  1 -> 1 [label="a"]
-  2 [label="s2"]
-  2 -> 0 [label="b"]
   3 -> 1 [label="a"]
   3 -> 0 [label="b"]
+  }
+  2 [label="s2"]
+  2 -> 0 [label="b"]
 }
 EOF