- use one theme surface instead of several small ones
- add a theme without alphachannel
- D_ASSERTS in most important internal functions.
- lite_open() has some issues with the return value, should return last DFBResult, not a default
  one...
- Rewrite LITE_BOX_PARAMETER_CHECK so it automatically typecasts an entry to a LiteBox.
- Use LITE_BOX_PARAMETER_CHECK in public LiteBox APIs...
- More public parameter testing in window.c.


optimizations
- discard updates while window is invisible, just update once right before showing
- don't recreate the subsurface in lite_reinit_box_and_children(), use (in)validation (lazy recreation)
- apply the same methodology to other things, having a generic validation/invalidation framework