title: Ember.js : How to set context of an action helper?
body: <p>I added the example application.
  <a href="http://jsfiddle.net/Sly7/amG56/" rel="nofollow">http://jsfiddle.net/Sly7/amG56/</a></p>
  
  <p>Js:</p>
  
  <pre><code>App = Ember.Application.create();
  
  App.ApplicationController = Ember.ArrayController.extend({
    selectedBook: null
  });
  
  App.ApplicationView = Ember.View.extend({
  
    actions: {
      selectBook: function(book) {
        this.get('controller').set("selectedBook", book);
      },
  
      cancel: function(book) {
        alert(book);
      }
    }
  });
  
  App.Book = Em.Object.extend({
    name: null
  });
  </code></pre>
  
  <p>Template:</p>
  
  <pre><code>&lt;script type="text/x-handlebars"&gt;
    {{#each book in books}}
      &lt;a {{action "selectBook" book target="view"}} href="#"&gt;select {{book.name}}&lt;/a&gt;&lt;br /&gt;
    {{/each}}
    &lt;hr /&gt;
    Selected Book: {{selectedBook.name}}
    &lt;br /&gt;
    &lt;a {{action "cancel" selectedBook target="view"}} href="#"&gt;cancel selected book&lt;/a&gt;
  &lt;/script&gt;
  </code></pre>
  
  <p>​</p>
  
  <p>Select one of the books. You will see that name of the book will be displayed. But the "cancel selected book" link does not work.</p>
  
  <p>I think the problem is context of the action helper does not change when a book is selected.</p>
  
  <p>How do I implement an action helper which has a changing context? Or is it a bug? </p>