Fixes bug #502.

The ownership of the editor returned by the Python override of
QAbstractItemDelegate.createEditor(...) is now transferred to C++.

A test was added to simulate the situation that triggers the bug,
instead of relying on an example with a view, model and editable cells.

See: http://bugs.openbossa.org/show_bug.cgi?id=502

Reviewed by Lauro Moura <lauro.neto@openbossa.org>
Reviewed by Renato Araújo <renato.filho@openbossa.org>

PySide/QtGui/typesystem_gui_common.xml

@@ -3047,6 +3047,9 @@
       <modify-argument index="1">
         <define-ownership owner="c++"/>
       </modify-argument>
+      <modify-argument index="return">
+        <define-ownership class="native" owner="c++"/>
+      </modify-argument>
     </modify-function>
   </object-type>
   <object-type name="QTableWidgetItem" >