Uniforms/constants aren't shared in D3D, let's not pretend they are.
D3D: Use fixed constant registers for pixel shader constants
D3D: Use fixed constant registers for vertex shaders too.
Some renaming
DX9: Not much point in tracking dirtiness per shader now that all constants are shared.
DX9: "Linked" shaders are now pointless, so remove them.
D3D: Assorted cleanup. Add a missing register specification.
Merge pull request #6873 from hrydgard/d3d-shader-cleanup

D3D shader cleanup - remove LinkedShaders and use fixed constant slots