title: Rails validation on content type not working with Paperclip
body: <p>I have a validation in my Rails (3.1.4) model to make sure no one tries to upload anything malicious in leiu of their profile image, but when I try to upload a jpeg, the validation is triggering.  I'm using the Paperclip gem and I'm unsure if that is having an impact.</p>
  
  <p>validation in user.rb model</p>
  
  <pre><code>validates_attachment_content_type :profile_image, :content_type =&gt; ['image/jpeg', 'image/png', 'image/gif'], :message =&gt; "Only jpeg, gif and png files are allowed for profile pictures"
  </code></pre>
  
  <p>When I look at the properties of the jpeg locally (Windows O/S):</p>
  
  <ul>
  <li>Item type = JPEG image</li>
  <li>Type of file: JPEG image (.jpg)</li>
  </ul>
  
  <p>Am I doing something wrong in my validation?  </p>
  
  <p>Also, when it triggers, it puts the model and field name before the message.  Is there a way to avoid that?  ie 'Profile image profile image content type Only jpeg, gif and png files are allowed for profile pictures'</p>
  
  <p>Thank you! </p>