function register($username, $email, $password)
// register new person with db
// return true or error message
{
 // connect to db
  $conn = db_connect();
  if (!$conn)
    return 'Could not connect to database server - please try later.';
  // check if username is unique 
  $result = mysql_query("select * from user where username='$username'"); 
  if (!$result)
     return 'Could not execute query';
  if (mysql_num_rows($result)>0) 
     return 'That username is taken - go back and choose another one.';

  // if ok, put in db
  $result = mysql_query("insert into user values 
                         ('$username', password('$password'), '$email')");
  if (!$result)
    return 'Could not register you  in database - please try again later.';

  return true;
}