title: Rails 3 - get full error message for one field
body: <p>I have <code>user.errors</code> which gives all errors in my controller. So, i have the field <code>:user_login</code> which has its error(s). How can i get <strong>full</strong> error messages from <code>user.errors</code> ONLY for that field? </p>
  
  <p>I can get just text of this field like that:</p>
  
  <pre><code>user.errors[:user_login] # Gives that 'can't be empty'
  </code></pre>
  
  <p>But i really want to do something like that</p>
  
  <pre><code>user.errors.get_full_message_for_field[:user_login] # 'Your login can't be empty'
  </code></pre>