Arc editor : use QPropertyUndoCommand instead of ChangePartCommand

git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@4066 bfdf4180-ca20-0410-9c96-a3a8aa849046

sources/editor/polygoneditor.h

@@ -17,9 +17,15 @@
 */
 #ifndef POLYGON_EDITOR_H
 #define POLYGON_EDITOR_H
+
 #include "elementitemeditor.h"
+#include <QTreeWidget>
+#include <QCheckBox>
+
 class PartPolygon;
 class StyleEditor;
+class QTreeWidget;
+
 /**
 	This class provides a widget to edit polygons within the element editor.
 */