Fix incorrect binding in test functions.

`env` wasn't being closed over properly.

Author: cloudhead

lib/vows.js

@@ -331,11 +331,11 @@ function addVows(tests) {
                         // before calling the inner context. Else, just run the inner context
                         // synchronously.
                         if (topic) {
-                            topic.addListener("success", function (vow, ctx) {
+                            topic.addListener("success", function (vow, ctx, env) {
                                 return function (val) {
                                     return run(new(Context)(vow, ctx, env), lastTopic);
                                 };
-                            }(vow, ctx));
+                            }(vow, ctx, env));
                         } else {
                             run(new(Context)(vow, ctx, env), lastTopic);
                         }

test/vows-test.js

@@ -237,6 +237,26 @@ vows.describe("Vows").addVows({
             }
         }
     }
+}).addVows({
+    "Sibling contexts": {
+        "'A', with `this.foo = true`": {
+            topic: function () {
+                this.foo = true;
+                return this.foo;
+            },
+            "should have `this.foo` set to true": function (res) {
+                assert.equal(res, true);
+            }
+        },
+        "'B', with nothing set": {
+            topic: function () {
+                return this.foo;
+            },
+            "should have `this.foo` be undefined": function (res) {
+                assert.isUndefined(res);
+            }
+        }
+    }
 }).addVows({
     "A 2nd test suite": {
         topic: function () {