[WIN32K]

[WIN32K]
  - work directly with bitmap bits when alpha blending icons. This is permitted, those are API bitmaps.
  - Do not create a stretched copy of source surface in EngAlphaBlend, handle stretching in DIB functions.
  - Do so.
  - Simplify DIB alpha blending for 24 and 32 bpp, implement generic alpha blend support for other depth.

svn path=/branches/reactos-yarotows/; revision=48483