refactor(Angular): add isPromiseLike helper function

This can be used internally to remove the repeating pattern of `obj && obj.then`. For now, I don't see a good reason to expose this in angular's public interface.

Conflicts:
	src/Angular.js

src/.jshintrc

@@ -50,6 +50,7 @@
     "isFile": false,
     "isBlob": false,
     "isBoolean": false,
+    "isPromiseLike": false,
     "trim": false,
     "isElement": false,
     "makeMap": false,

src/Angular.js

@@ -46,6 +46,7 @@
     isFile: true,
     isBlob: true,
     isBoolean: true,
+    isPromiseLike: true,
     trim: true,
     isElement: true,
     makeMap: true,
@@ -582,6 +583,11 @@ function isBoolean(value) {
 }
 
 
+function isPromiseLike(obj) {
+  return obj && isFunction(obj.then);
+}
+
+
 var trim = (function() {
   // native trim is way faster: http://jsperf.com/angular-trim-test
   // but IE doesn't have it... :-(

src/ng/http.js

@@ -954,7 +954,7 @@ function $HttpProvider() {
       if (cache) {
         cachedResp = cache.get(url);
         if (isDefined(cachedResp)) {
-          if (cachedResp.then) {
+          if (isPromiseLike(cachedResp)) {
             // cached request has already been sent, but there is no response yet
             cachedResp.then(removePendingReq, removePendingReq);
             return cachedResp;

src/ng/httpBackend.js

@@ -132,7 +132,7 @@ function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDoc
 
     if (timeout > 0) {
       var timeoutId = $browserDefer(timeoutRequest, timeout);
-    } else if (timeout && timeout.then) {
+    } else if (isPromiseLike(timeout)) {
       timeout.then(timeoutRequest);
     }
 

src/ng/q.js

@@ -303,7 +303,7 @@ function qFactory(nextTick, exceptionHandler) {
             } catch(e) {
               return makePromise(e, false);
             }
-            if (callbackOutput && isFunction(callbackOutput.then)) {
+            if (isPromiseLike(callbackOutput)) {
               return callbackOutput.then(function() {
                 return makePromise(value, isResolved);
               }, function(error) {
@@ -328,7 +328,7 @@ function qFactory(nextTick, exceptionHandler) {
 
 
   var ref = function(value) {
-    if (value && isFunction(value.then)) return value;
+    if (isPromiseLike(value)) return value;
     return {
       then: function(callback) {
         var result = defer();