Fix slide show animation so that cross fades work.

 Bug 7961297
 Removed the "Additive" blending, which didn't do anything, even in
 OpenGL ES 1.1 implementation. Modified the texturing to
 change the color of the pixels based on the supplied alpha
 rather than modifying the alpha. This appears to match the
 implementation in the OpenGL ES 1.1 pipeline.

Change-Id: I52491af1a8a2d727968e4e805bc4bc61647f5cf2
5 files changed