Adding failing test - Two level hierarchy

Hi Gordon,

As discussed, added a test with Post hasMany Comments hasMany Lines. It fails when both Comments and Lines are set with {embedded: always}.

With the change I suggested in my note earlier, all tests are successful.

```javascript
function createNestedPromise(node) {
      var promise = node.promise(store, adapter);
      if((node.children.length > 0) && (promise)){  // Here
        promise = promise.pipe(function() {
          var childPromises = Ember.A(node.children.map(createNestedPromise)).compact();
          return jQuery.when.apply(jQuery, childPromises);
        });
      }
      return promise;
    }
```


Thanks
PJ