The whole control structures in directx.c get terribly confusing with
the various codepaths for texturing and different shader
implementations. It is also hard to reflect the shader model
decisions this way too. This patch moves the shader specific parts of
the caps code into the shader backend where we can set our caps
dependent of the shader model decisions and without complex caps flag
checks.

Generating the shader ID and parts of the shader prolog and epilog was
done by the common vertexshader.c / pixelshader.c, which is ugly.

This patch doesn't get rid of all the uglyness, somewhen we'll still
have to sort out the relationship of [arb|glsl]_generate_shader and
[arb|glsl]_generate_declarations.

ddraw: Don't clear the return value anymore, we fill the fields anyway, also a test for the behaviour.

Adds rudimentary test for 8 bit mode ddraw (palettized primary surface). Tests 
things like GetDC and its palette handling and SetPalette affected by patches 
that follow.