feat($q): added support to promise notification

It is now possible to notify a promise through deferred.notify() method.
Notifications are useful to provide a way to send progress information
to promise holders.

src/ng/q.js

@@ -199,7 +199,7 @@ function qFactory(nextTick, exceptionHandler) {
               var callback;
               for (var i = 0, ii = callbacks.length; i < ii; i++) {
                 callback = callbacks[i];
-                value.then(callback[0], callback[1]);
+                value.then(callback[0], callback[1], callback[2]);
               }
             });
           }
@@ -212,8 +212,25 @@ function qFactory(nextTick, exceptionHandler) {
       },
 
 
+      notify: function(progress) {
+        if (pending) {
+          var callbacks = pending;
+
+          if (pending.length) {
+            nextTick(function() {
+              var callback;
+              for (var i = 0, ii = callbacks.length; i < ii; i++) {
+                callback = callbacks[i];
+                callback[2](progress);
+              }
+            });
+          }
+        }
+      },
+
+
       promise: {
-        then: function(callback, errback) {
+        then: function(callback, errback, progressback) {
           var result = defer();
 
           var wrappedCallback = function(value) {
@@ -234,10 +251,18 @@ function qFactory(nextTick, exceptionHandler) {
             }
           };
 
+          var wrappedProgressback = function(progress) {
+            try {
+              result.notify((progressback || defaultCallback)(progress));
+            } catch(e) {
+              exceptionHandler(e);
+            }
+          };
+
           if (pending) {
-            pending.push([wrappedCallback, wrappedErrback]);
+            pending.push([wrappedCallback, wrappedErrback, wrappedProgressback]);
           } else {
-            value.then(wrappedCallback, wrappedErrback);
+            value.then(wrappedCallback, wrappedErrback, wrappedProgressback);
           }
 
           return result.promise;
@@ -359,7 +384,7 @@ function qFactory(nextTick, exceptionHandler) {
    * @param {*} value Value or a promise
    * @returns {Promise} Returns a promise of the passed value or promise
    */
-  var when = function(value, callback, errback) {
+  var when = function(value, callback, errback, progressback) {
     var result = defer(),
         done;
 
@@ -381,15 +406,26 @@ function qFactory(nextTick, exceptionHandler) {
       }
     };
 
+    var wrappedProgressback = function(progress) {
+      try {
+        return (progressback || defaultCallback)(progress);
+      } catch (e) {
+        exceptionHandler(e);
+      }
+    };
+
     nextTick(function() {
       ref(value).then(function(value) {
         if (done) return;
         done = true;
-        result.resolve(ref(value).then(wrappedCallback, wrappedErrback));
+        result.resolve(ref(value).then(wrappedCallback, wrappedErrback, wrappedProgressback));
       }, function(reason) {
         if (done) return;
         done = true;
         result.resolve(wrappedErrback(reason));
+      }, function(progress) {
+        if (done) return;
+        result.notify(wrappedProgressback(progress));
       });
     });