- 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