title: Enable/disable drop down list based on another drop down list
body: <p>I have 2 drop down list</p>
  
  <pre><code>&lt;select id="servergroup" multiple="multiple"&gt;             
    &lt;option value="P1"&gt;P1&lt;/option&gt;
    &lt;option value="P2"&gt;P2&lt;/option&gt;
    &lt;option value="P3"&gt;P3&lt;/option&gt;
    &lt;option value="P4"&gt;P4&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select id="servername" multiple="multiple"&gt;
    &lt;option value="s597ap233"&gt;s597ap233&lt;/option&gt;
    &lt;option value="s597dp392"&gt;s597dp392&lt;/option&gt;
    &lt;option value="s397dp095"&gt;s397dp095&lt;/option&gt; 
  &lt;/select&gt;
  </code></pre>
  
  <p>I want that the second drop down list should get enabled only if we choose a value in the first drop down list. It should again get disabled if we deselect the value from the first drop down list.
  May I know how can this be achieved using jQuery?</p>