title: "Error": errors.add don't show only the message in locales/xx.yml
body: <p>I have a method in the model is to check if one is suspicious attachment before to make the upload , in case , if his ends with . Bat . With . Exe , . Src or. Cmd .</p>
  
  <p>I want to show a message if his file is suspicious .
  I'm portuguese , so I use one file of translate .</p>
  
  <p>The method is:</p>
  
  <pre><code>def suspicious_attachment
    if ends_with? '.bat', '.com', '.exe', '.src', '.cmd'
      errors.add(:attachment_file_name, I18n.t('errors.messages.suspicious_attachment', :value =&gt; attachment.path[-4..-1]))
      errors.add_to_base(I18n.t('errors.messages.suspicious_attachment', :value =&gt; attachment.path[-4..-1]))
      errors.add(:attachment_file_name)
    end
  end
  </code></pre>
  
  <p>Which returns :</p>
  
  <p>Attachments attachment file name is not allowed to upload . With
  Attachments attachment file name is not valid
  Attachments base is not allowed to upload . With</p>
  
  <p>I do not want to show Those words : "Attachments attachment file name" and "Attachments base ."</p>
  
  <p>I do not understand why these words appear.</p>
  
  <p>Sorry for my english.</p>
  
  <p>Thanks</p>