[vdr] [path] vdr-1.6 better spu on ff card

[matthieu castet]

Hi,

this patch try to handle case where the osd is limited (for example on ff card).
For that it try to split area, count the really needed bpp (all transparent index can be merged together and will with my previous patch in osd.c).

Also it fix a bug in the current version : removing all the transparent baground area is ok only if it is recomputed at each draw. Otherwise a highlight request can happen outside the computed area.

With this patch I can navigate in dvd menu that produce oeOutOfMemory before.

Matthieu