title: Knockout checked binding issue
body: <p>I'm having a problem with checkbox bindings not quite working with KnockoutJS 2.0.  I have an array of objects.  One of the properties of those objects is an array of different objects.  In the child objects there are a few properties, one of which is a boolean.  I build a list for each parent object and under each parent I show the children.  For each list of children I have two views, a read only and an edit view.  In the read only I have images that represent whether or not the item is checked based on the boolean property.  This works and if I update the boolean value through the console, I'm seeing what I would expect--the image goes away or displays based on the value I assign.  In the edit view, the images are replaced with a checkbox.  I see the same behavior when I update the value through the console--it is checked when I expect it to be and not when I don't.  The problem comes in when I check or uncheck the checkbox.  Doing this doesn't change the underlying value the checkbox is bound to.</p>
  
  <p>Here's the basic idea of my data.</p>
  
  <pre><code>[
      {
          "xxx": "yyy",
          "xxx": "yyy",
          ...
          "Displays": [
              {
              "xxx": "yyy",
              ...
                  "Excluded": false,
              },
              {
              "xxx": "yyy",
               ...
                  "Excluded": true,
              }
          ],
      }
  ]
  </code></pre>
  
  <p>Here's the binding</p>
  
  <pre><code>&lt;input type="checkbox" data-bind="checked: !Excluded()" /&gt;
  </code></pre>