Pass all parameters to ComboBox.set_row_separator_func()

With PyGTK, the func and data parameters to ComboBox.set_row_separator_func()
had defaults [1]. With GTK3+pygi both values must be passed [2].

[1] http://developer.gnome.org/pygtk/stable/class-gtkcombobox.html#method-gtkcombobox--set-row-separator-func
[2] http://developer.gnome.org/gtk/stable/GtkComboBox.html#gtk-combo-box-set-row-separator-func

[replaced description]
Signed-off-by: Sascha Silbe <silbe@activitycentral.com>

src/sugar3/graphics/combobox.py

@@ -39,7 +39,7 @@ class ComboBox(gtk.ComboBox):
                                     gobject.TYPE_BOOLEAN)
         self.set_model(self._model)
 
-        self.set_row_separator_func(self._is_separator)
+        self.set_row_separator_func(self._is_separator, None)
 
     def get_value(self):
         """
@@ -166,5 +166,5 @@ class ComboBox(gtk.ComboBox):
         """
         self._model.clear()
 
-    def _is_separator(self, model, row):
+    def _is_separator(self, model, row, data):
         return model[row][3]