add traceur test suite

test/fixtures/traceur/Yield/ForLexicallyNestedGenerator.js

@@ -0,0 +1,15 @@
+function* forLexicallyNestedGenerator() {
+  yield* (function*() { yield [1,2,3]; yield* [4,5,6]; })();
+}
+
+function accumulate(iterator) {
+  var result = '';
+  for (var value of iterator) {
+    result = result + String(value);
+  }
+  return result;
+}
+
+// ----------------------------------------------------------------------------
+
+assert.equal('1,2,3456', accumulate(forLexicallyNestedGenerator()));