title: :prompt appearing in collection_select when a records value is expected
body: <p>Sorry, this may seem like a simple issue, but: I have a collection_select element that is called via ajax from a _updateregions.html.erb file for creating and editing records that looks like:</p>
  
  <pre><code>&lt;%= collection_select(:wine, :wineregionid,  regions,  :wineregionid, :regionname,
                      options = {:selected =&gt; :wineregionid, :prompt   =&gt; "Select a Region"}
   ) %&gt;
  </code></pre>
  
  <p>The problem is, when editing an existing record, the prompt is appearing by default instead on the records value. When I remove the :prompt, it works fine... question is, how can I make this work for both the New and Edit case?
  According to <a href="http://api.rubyonrails.org/classes/ActionView/Helpers/FormOptionsHelper.html" rel="nofollow">http://api.rubyonrails.org/classes/ActionView/Helpers/FormOptionsHelper.html</a> I think I'm doing it right....</p>
  
  <blockquote>
    <p>collection_select(object, method,
    collection, value_method, text_method,
    options = {}, html_options = {})</p>
    
    <p>Returns  and  tags for
    the collection of existing return
    values of method for object‘s class.
    The value returned from calling method
    on the instance object will be
    selected. If calling method returns
    nil, no selection is made without
    including :prompt or :include_blank in
    the options hash.</p>
  </blockquote>