title: Knockout: Mapping/binding JSON issue
body: <p>i'm trying a basic hello work example getting json, auto mapping it and then binding to an observable, I'm sure i'm getting something basic wrong.</p>
  
  <p>JSON returned from ajax call</p>
  
  <pre><code>"{\"Content\":\"hello world\"}"
  </code></pre>
  
  <p>JS</p>
  
  <pre><code>function ViewModel() {
  var self = this;
  
  self.message = ko.observable();
  
  $.getJSON("/home/getmessage", function (response) {
      var mapped = ko.mapping.fromJSON(response);
      self.message(mapped.Content);
  });
  };
  
  ko.applyBindings(new ViewModel());
  </code></pre>
  
  <p>I'm getting the following in place of 'hello world' that i was expecting</p>
  
  <pre><code>function c(){if(0&lt;arguments.length){if(!c.equalityComparer||!c.equalityComparer(d,arguments[0]))c.I(),d=arguments[0],c.H();return this}a.U.La(c);return d}
  </code></pre>