fix($evalAsync): have only one global async queue

Having one async queue per scope complicates the matters when users wish to do
partial scope updates, since many services put events on the rootScope. By
having single queue the programing model is simplified.

src/ng/rootScope.js

@@ -195,7 +195,6 @@ function $RootScopeProvider(){
         child['this'] = child;
         child.$$listeners = {};
         child.$parent = this;
-        child.$$asyncQueue = [];
         child.$$watchers = child.$$nextSibling = child.$$childHead = child.$$childTail = null;
         child.$$prevSibling = this.$$childTail;
         if (this.$$childHead) {
@@ -362,7 +361,7 @@ function $RootScopeProvider(){
       $digest: function() {
         var watch, value, last,
             watchers,
-            asyncQueue,
+            asyncQueue = this.$$asyncQueue,
             length,
             dirty, ttl = TTL,
             next, current, target = this,
@@ -371,18 +370,19 @@ function $RootScopeProvider(){
 
         beginPhase('$digest');
 
-        do {
+        do { // "while dirty" loop
           dirty = false;
           current = target;
-          do {
-            asyncQueue = current.$$asyncQueue;
-            while(asyncQueue.length) {
-              try {
-                current.$eval(asyncQueue.shift());
-              } catch (e) {
-                $exceptionHandler(e);
-              }
+
+          while(asyncQueue.length) {
+            try {
+              current.$eval(asyncQueue.shift());
+            } catch (e) {
+              $exceptionHandler(e);
             }
+          }
+
+          do { // "traverse the scopes" loop
             if ((watchers = current.$$watchers)) {
               // process our watches
               length = watchers.length;

test/ng/rootScopeSpec.js

@@ -441,7 +441,7 @@ describe('Scope', function() {
       child.$evalAsync(function(scope) { log += 'child.async;'; });
       child.$watch('value', function() { log += 'child.$digest;'; });
       $rootScope.$digest();
-      expect(log).toEqual('parent.async;parent.$digest;child.async;child.$digest;');
+      expect(log).toEqual('parent.async;child.async;parent.$digest;child.$digest;');
     }));
 
     it('should cause a $digest rerun', inject(function($rootScope) {