title: multiple=multiple in cakephp creates additional hidden field
body: <p>I have a <code>select-option</code> field in my form as below:</p>
  
  <pre><code>&lt;div&gt;
   &lt;?php echo $this-&gt;Form-&gt;input('employee_id', array('label' =&gt; 'Hi','multiple'=&gt;true,'id'=&gt;'multiselect', 'options' =&gt; $employee));?&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>But when I checked the page-source, it produces an additional <code>hidden</code> field in my form.</p>
  
  <pre><code>&lt;div&gt;
  &lt;div class="input select"&gt;
  &lt;label for="multiselect"&gt;Hi&lt;/label&gt;
  &lt;input type="hidden" name="data[Participant][employee_id]" value="" id="multiselect_"/&gt;
  &lt;select name="data[Participant][employee_id][]" multiple="multiple" id="multiselect"&gt;
  &lt;option value="1"&gt;A1&lt;/option&gt;
  &lt;option value="2"&gt;A2&lt;/option&gt;
  &lt;option value="3"&gt;A3&lt;/option&gt;
  &lt;option value="4"&gt;A4&lt;/option&gt;
  &lt;/select&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Whats the reason ? I am not able to get the employee id array due to this in my POST data.</p>