title: Rails fields_for ignores :disabled field
body: <p>I'm using Rails 4.1.4 and have the basic structure for nested attributes using fields_for. I've noticed that <strong>disabled</strong> option is totally ignored for the fields inside the fields_for block. </p>
  
  <p>In my code example the first text_field is disabled and the one after fields_for is not. What am I missing here? </p>
  
  <pre><code>   ...    
      &lt;%= f.text_field :response_given, disabled: true %&gt;
      &lt;%= f.fields_for :meta_set do |mf| %&gt;
        &lt;%= mf.text_field :name, disabled: true %&gt;
        ...
  </code></pre>