create_simple_positioner() uses absolute popup coordinates

When a popup is created, moved by gtk_window_move() and shown, it's invisible or positioned wrongly. It's because create_simple_positioner() calculates popup position as global but it should be local.

For instance when I open a popup which starts at 800,100 and create it's child popup placed at 40,40, the child is positioned as -760,-60 and is not shown.