The HLSL compiler refuses to use NaN and +/-Inf values in pre-SM4
shaders, claiming that those are unsupported in this shader model.
However, vsa.exe happilly generates them, the required strings in the
shader code are 1.#QNAN and 1.#INF. Native d3d9 happily loads such a
shader.

This is essentially a revert of cd7825c8,
with proper precision.