title: User registration form validation in drupal 7
body: <p>Drupal 7 comes with the built-in user registration form (user/register). I use this form for new users to register. Which is quite obvious. Now the problem is, and I find it hard to believe that it isn't there, I need some validating.</p>
  
  <p>When a new user completes the form and hits submit, the account is being created. Good.</p>
  
  <p><strong>But</strong>: when a user completes the form and hits submit, but the <strong>email address or username is already in use</strong>, the pages just reloads and the user is not being created, which is good, but theres no warning on what he has to change in the form what so ever.</p>
  
  <p>I find it strange that this is not standard.</p>
  
  <p>Could anyone provide me some help? I really have no clue...</p>