HASTE V115 BETA 15 - BLOOM SHIMMER + COLOURED LIGHT STABILITY

Bloom (final.fsh)
- colortex4 (bloom mask) is now RGBA16F. As 8-bit, the mip-averaged mask of small lights was rounded to a few
  steps and flickered as the light moved on screen.
- Mip footprint is now ~0.65 sigma (was ~1.9 sigma), so a moving light no longer hops between large mip texels.
  The blur radius is compensated (kernel 0.94 sigma). Mip level never goes below 1.
- The "bloom dims over the emitter" term reads mip 2 instead of the raw, aliased pixel.

Coloured lighting
- lib/colored_light.glsl: the light volume is trilinearly interpolated by hand (8 taps on texel centres), so it
  is smooth whatever filter mode the driver uses.
- shadowcomp.csh: thin-block veto -1 -> -3, so slabs/stairs need ~14 frames without an inside face before they
  can flip to "wall" (grazing sun used to flip them within 6 frames, flashing light through/around them).

Not compiled or tested in-game here. Test in Iris on the Ethereal preset.
