Make flash messages work for route resources

Hi there,
I realised that when setting a flash message and then transitioning into a route defined as resource, the flash message is lost.

```javascript
App.Router.map(function() {
  this.resource('posts', { path: '/posts' }, function() {
    this.route('new');
  });
});
```

```javascript
this.flashMessage("Create a new post");
this.transitionTo('posts.new');
```
For whatever reason the "activate" hook is called twice.(Probably once for PostsRoute, and once for PostNewRoute in the example above).

The first time it is called with *routeName* "post", second time with "post.new". 

The problem is, that the first time the hook is called the message gets set, so on the second time it is lost. I fixed it by comparing the *routeName* to the transition's *targetName*.