GPUMC - Partial fix for lookup table woes

SURPRISE: it was an alignment issue. Turns out computers like things on
word boundaries and I forgot that - AGAIN

However, the 2nd, 3rd, 4th, and 5th entries are still broken. Yay.
GPUMC - Waste more time dealing with broken tex
GPUMC - Fix lookup table

For real this time. Turns out the issue was using texture instead of
texelFetch in the geometry shader.