bugfix(assertAsync): add promiseLike support for angularJS promises

implement a promiseLike method so libraries using non-browser promise
implementations can still utilize assertAsync functionality.

Fixes: #1612

src/core/AsyncExpectation.js

@@ -19,7 +19,7 @@ getJasmineRequireObj().AsyncExpectation = function(j$) {
       throw new Error('expectAsync is unavailable because the environment does not support promises.');
     }
 
-    if (!j$.isPromise(this.actual)) {
+    if (!j$.isPromiseLike(this.actual)) {
       throw new Error('Expected expectAsync to be called with a promise.');
     }
 

src/core/base.js

@@ -120,7 +120,11 @@ getJasmineRequireObj().base = function(j$, jasmineGlobal) {
   };
 
   j$.isPromise = function(obj) {
-    return typeof jasmineGlobal.Promise !== 'undefined' && obj && obj.constructor === jasmineGlobal.Promise;
+    return typeof jasmineGlobal.Promise !== 'undefined' && !!obj && obj.constructor === jasmineGlobal.Promise;
+  };
+
+  j$.isPromiseLike = function(obj) {
+    return !!obj && j$.isFunction_(obj.then);
   };
 
   j$.fnNameFor = function(func) {