Even the comment says it's 8.8, so no need for 32 bits for each value.
It seems to have made a very small improvement to my glsl stub test, but
it's probably just noise (< 0.5%). However, having it "officially" 16
bits means that cached values can be 16 bits thus reducing struct sizes
when I rework lightmap surface data (taking the cache from 16 to 8
bytes).
0a9cc91503