DP2ADD is valid on pshaders 2.0 and above, has 4 parameters.
TEXLDD is valid on pshaders 2.x and above, has 5 parameters.

There are a total of 17 instructions without a destination token. Of
those 9 have num_params != 0, which means that we will not process any
of them correctly, because we assume the first token (if present) is a
destination token.

Those are basically all the flow control instructions, which we plan to
support very soon. They have source tokens, and no destination. Add a
flag that marks them up to the ins table. Use this flag in the trace
pass, and generation pass.

GLSL uniforms have as scope the entire program.
To prevent conflicts, name pshader and vshader constants differently.
Based on a patch by Jason Green.

- track sampler declarations and store the sampler usage in reg_maps structure
- store a fake sampler usage for 1.X shaders (defined as 2D sampler)
- re-sync glsl TEX implementation with the ARB one (no idea why they diverged..)
- use sampler type in new TEX implementation to support 2D, 3D, and Cube sampling
- change drawprim to bind pixel shader samplers

Additional improvements:
- rename texture limit to texcoord to prevent confusion
- add sampler limit, and use that for samplers - *not* the same as texcoord above

Anything with a swizzle has to be casted to vec4, or it won't work properly.
There's multiple ways to do this, for the moment pick the easiest one.