doFlush returns the same RouteCollection instance now, so there's no …

…need to add the sub-collection routes to itself

src/Silex/ControllerCollection.php

@@ -210,7 +210,7 @@ private function doFlush($prefix, RouteCollection $routes)
                 $routes->add($name, $controller->getRoute());
                 $controller->freeze();
             } else {
-                $routes->addCollection($controller->doFlush($prefix.$controller->prefix, $routes));
+                $controller->doFlush($prefix.$controller->prefix, $routes);
             }
         }