title: Adding disabled option in codeigniter form_dropdown
body: <p>I'm trying to figure out how to add a disabled option in my dropdown, using codeIgniter. New to CI, and I've tried googling it a bit, but couldn't find an answer.</p>
  
  <p>My code for a dropdown looks like this:</p>
  
  <pre><code>    echo form_dropdown('category', array('0' =&gt; 'Choose a category...')  + $categories, '0');
  </code></pre>
  
  <p>This gives me a dropdown with all my options from the variable $categories, with "Choose a category..." (value 0) at top. Now how to I make the first one disabled? I know how to make it select a specific one, which I've set it to do here.</p>
  
  <p>Can anyone help me? Thanks</p>