Turns out that the name doesn't accurately describe what it does.
It is correct for images that come with their own palette or are true color.
But for images using the game palette it doesn't use the red channel to determine translucency but the palette index! Ugh...
This means it cannot be done with a simple operation in the shader because it won't get a proper source image. The only solution is to create a separate texture.
- replaced GLUs texture scaling with our own function. This is only used to scale down textures larger than what the hardware can handle so we do not need a dependency to an essentially deprecated library for it.
Due to autoexpansion to remove filtering artifacts their dimensions are not the same as for patches. But if the sprite hadn't been used yet this information won't have been set yet.
- removed gl_vid_compatibility. With the bump to 1.4 no hardware requiring this flag is supported anymore.
- disabled 16 bit framebuffers for the same reason. As a conseqence all code for rendering without stencil could also be removed.
