use instanceof to determine whether an object is a Q promise inside function Q

q.js

@@ -450,7 +450,7 @@ function Q(value) {
     // If the object is already a Promise, return it directly.  This enables
     // the resolve function to both be used to created references from objects,
     // but to tolerably coerce non-promises to promises.
-    if (isPromise(value)) {
+    if (value instanceof Promise) {
         return value;
     }