Remove stray global "tween".

d3.v2.js

@@ -2150,8 +2150,8 @@ function d3_transition(groups, id, time) {
         lock.active = id;
 
         tweens.forEach(function(key, value) {
-          if (tween = value.call(node, d, i)) {
-            tweened.push(tween);
+          if (value = value.call(node, d, i)) {
+            tweened.push(value);
           }
         });
 

src/core/transition.js

@@ -45,8 +45,8 @@ function d3_transition(groups, id, time) {
         lock.active = id;
 
         tweens.forEach(function(key, value) {
-          if (tween = value.call(node, d, i)) {
-            tweened.push(tween);
+          if (value = value.call(node, d, i)) {
+            tweened.push(value);
           }
         });