title: Make unique DWord constants, not concurrent to any TObject address
body: <p>I use Python4Delphi in D7. I want to pass object address as "handle" to Py part. E.g.<br>
  <code>h:= Integer(Pointer(Memo1));</code>. I also want to have special handle values, which mean some specials objects, e.g. <code>-1</code> means "current memo", <code>-2</code> means "next memo".</p>
  
  <p>How can I choose such few (I need 5) constants, which won't conflict with object adresses?
  E.g. </p>
  
  <ul>
  <li><code>-1</code> - can it be address of some TMemo (of other TObject)?</li>
  <li><code>-2</code> - can it be address of some TMemo?</li>
  <li>what else constants can I take which cannot be TMemo addresses?</li>
  </ul>