title: Set message for two unique fields
body: <p>I want to set a custom error message on both a username and an email field when the is_unique validation check fails.</p>
  
  <pre><code>$this-&gt;form_validation-&gt;set_message('is_unique', 'Username already registered, please log in!');
  
  $this-&gt;form_validation-&gt;set_message('is_unique', 'Email already registered, please log in!');
  </code></pre>
  
  <p>How will codeigniter decipher between the two? I've consulted the user guide and haven't found a solution. Is there a way to tell it the is_unique is for the username and then the next one is for the email?</p>
  
  <p>Thanks for your time.</p>