title: Knockout, previous value of select / dropdown
body: <p>I want to know what the previous value is from a Dropdown list.</p>
  
  <p>In the following html I can set the Options and the currently selected.</p>
  
  <pre><code>    &lt;select data-bind="options: group_128,
                         optionsText: 'description',
                         value: selectedgroup_128,
                         event: { change: selectionChanged_group_128 }"&gt;
      &lt;/select&gt;
  </code></pre>
  
  <p>in the Javascript / viewModel I do :</p>
  
  <pre><code>            selectionChanged_group_128 = function (data, event) {
              self.addItemClicked2(self.selectedgroup_128, event)
          };
  </code></pre>
  
  <p>At this point I want to know what the previous selected item was to send it to the addItemClicked2.</p>