title: form_for with datetime_select
body: <p>I am using Rails 3.1 and first time using <code>datetime_select</code>. I want to specify the minute select box to have 15 minute intervals rather than 1 minute intervals:</p>
  
  <pre><code>  &lt;%= f.datetime_select :start_datetime, :ampm =&gt; true, :start_minute =&gt; [0,15,30,45] %&gt;
  </code></pre>
  
  <p>But this doesn't seem to work. The <code>:start_datetime</code> is what the property is called in the <code>Event</code> model. Is it possible that this is a reserved word that is causing problems?</p>