fix($q): make instanceof work for $q promises

Closes: #13574
Closes: #13545

Author: thorn0

src/ng/q.js

@@ -566,11 +566,6 @@ function qFactory(nextTick, exceptionHandler) {
       throw $qMinErr('norslvr', "Expected resolverFn, got '{0}'", resolver);
     }
 
-    if (!(this instanceof Q)) {
-      // More useful when $Q is the Promise itself.
-      return new Q(resolver);
-    }
-
     var deferred = new Deferred();
 
     function resolveFn(value) {
@@ -586,6 +581,10 @@ function qFactory(nextTick, exceptionHandler) {
     return deferred.promise;
   };
 
+  // Let's make the instanceof operator work for promises, so that
+  // `new $q(fn) instanceof $q` would evaluate to true.
+  $Q.prototype = Promise.prototype;
+
   $Q.defer = defer;
   $Q.reject = reject;
   $Q.when = when;

test/ng/qSpec.js

@@ -221,6 +221,15 @@ describe('q', function() {
       expect(typeof promise.finally).toBe('function');
     });
 
+    it('should support the instanceof operator', function() {
+      /*jshint newcap: false */
+      var promise = new q(noop);
+      expect(promise instanceof q).toBe(true);
+      promise = q(noop);
+      expect(promise instanceof q).toBe(true);
+      /*jshint newcap: true */
+    });
+
 
     describe('resolve', function() {
       it('should fulfill the promise and execute all success callbacks in the registration order',