Re-sending this review request (code by Brian Hall)
https://github.com/imageworks/OpenColorIO/pull/278

- Enables GPU accelerated OCIO on iOS devices, including ipad.

One interesting implementation detail is that iOS mobile devices do
not support 3D textures. This code work around this issue by allowing
3D texture to be stored in a 2D "lut image". Trilinear interpolation
is then manually implemented using bilinear lookups.

-- Jeremy