make sure --dot=Bb is the same as --dot=b

* NEWS: Mention the fixed bug.
* src/twaalgos/dot.cc: Fix.
* wrap/python/tests/decompose.ipynb: Use it.

NEWS

@@ -57,6 +57,8 @@ New in spot 1.99.5a (not yet released)
 
   Bug fixes:
   * automaton parser was ignoring the "unambiguous" property.
+  * --dot=Bb should work like --dot=b, allowing us to disable
+    a B option set via an environment variable.
 
 New in spot 1.99.5 (2015-11-03)
 

src/twaalgos/dot.cc

@@ -119,6 +119,7 @@ namespace spot
 	      break;
 	    case 'b':
 	      opt_bullet = true;
+	      opt_bullet_but_buchi = false;
 	      break;
 	    case 'B':
 	      opt_bullet = true;