Simple unoptimized software skinning.

Does not take advantage of the possible reduction in state changes yet.
Save a couple of registers in the x86 vertex decoder jit by SIMD-ing prescale UV
Prepare transform pipeline for step by step decoding
Decode step by step when sw skinning
Enable the softskinning optimizations that let us merge drawcalls
No reason to involve the FPU when loading matrices
Vtx dec jit: Combine the scale and offset registers to save 1 more xmm register.
Optimize software skinning for x86.

Can't seem to get a win on Windows vs hardware skinning though, even though
draw calls drop by 2/3rd...
Delete obsolete code