Previously the popup buffer state was stored inside the group
panel layout instead of the window layout. This caused
overdraw for popups and the underlying window. To fix that now
all popups are stored inside the root window panel layout
and everything is drawn correctly.
While dividing previously spared me from a lot of work and problems
it is probably best to have everything working for every or as many
platforms as possible. Some platforms fail to provide good ways
to support everything (e.g.:X11 does not have pixmap clipping with
different width/height or alpha-blending) but all OpenGL demos
outside allegro (needs some additional work) should be able to run.
