title: CakePHP containable, group by in containable
body: <p>I have a table called People</p>
  
  <p>Like this:</p>
  
  <pre><code>ID    BillID    FirstName    LastName
  1       1           x            y
  2       1           z            t
  3       2           v            w
  </code></pre>
  
  <p>The relation is one to many (each Bill has many People)</p>
  
  <p>so I want to paginate this way:</p>
  
  <p>I want to have all people of (for instance) 5 different Bills in each page</p>
  
  <p>How should I make the query?!</p>