title: User message not showing in product view page
body: <p>In one of the Magento store, I have to restrict customers to add a product more the one time.
  I checked with the cart and pass an error to the customer. But Magento does not show any message in product view page.</p>
  
  <pre><code>Mage::getSingleton('core/session')-&gt;addNotice('You have already added this product in your cart');
  </code></pre>
  
  <p>Check the above code, I placed it in controller file. I thought it was correct. Let me know what I missed.</p>