This adds code for handling fixed function fragment processing with the
GL_ATI_fragment_shader extension. This is a sort-of programmable
interface for fragment processing at the level of shader model 1.4 in
d3d. This code is of use on r200, r250 and r280 cards(radeon 8500 to
9200) which do not support GL_ARB_fragment_program, but support pixel
shader 1.4 on Windows. This code is somewhat a counterpart to the
existing fragment processing code using GL_NV_register_combiners and
GL_NV_texture_shader.

Since the shader backend implementations might track opengl resources in
their private data inform them about reset calls. For example, the atifs
backend keeps track of the replacement shaders, which are lost during an
opengl context recreation.

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.