fixed a bug with MultiArcs + invalid test in plugin gv

@@ -2435,12 +2435,12 @@ class Transition (Node) :
         if input :
             for place, label in self.input() :
                 try :
-                    place.check(v.value for v in iterate(label.bind(binding)))
+                    place.check(v for v in iterate(label.flow(binding)))
                 except ValueError :
                     return False
         for place, label in self.output() :
             try :
-                place.check(v.value for v in iterate(label.bind(binding)))
+                place.check(v for v in iterate(label.flow(binding)))
             except ValueError :
                 return False
         return True

@@ -22,6 +22,11 @@ GraphViz; we can also draw the state graph:
 
 >>> for engine in ('neato', 'dot', 'circo', 'twopi', 'fdp') :
 ...     n.draw(',test-gv-%s.png' % engine, engine=engine)
+Graph(...)
+Graph(...)
+Graph(...)
+Graph(...)
+Graph(...)
 >>> s = StateGraph(n)
 >>> s.build()
 >>> s.draw(',test-gv-graph.png')
@@ -204,6 +209,7 @@ def extend (module) :
             ...         attr['label'] = '%s\\n%s' % (trans.name, trans.guard)
             >>> n.draw(',net-with-colors.png',
             ...        place_attr=draw_place, trans_attr=draw_transition)
+            Graph(...)
 
             @param filename: the name of the image file to create
             @type filename: `str`