[Mesa-dev] glsl fp64 fixes.

[Dave Airlie]

I've been trying to get GL41-CTS.gpu_shader_fp64.varyings to
pass on mesa for a while now on radeonsi/r600.

I finally got it to pass, so this is the first round of changes.

The second round are all st/glsl->tgsi convertor changes, so I
decided to post the GLSL changes first.

The main changes are ARB_vertex_attrib_64bit related, where
the vertex input locations are counted different than the other
areas, but it also fixes transform feedback with doubles.

It also introduces a new types helper and uses it in a couple
of places.

Dave.