These add a new transform type, AllocationTransform, which is useful
in mapping HDR color ranges into LDR code spaces. Two options are
supported: a uniform allocation, and a log-2 allocation, and the
specific math corresponds to the gpu allocation options already used
internally. This transform is useful for applying LUTs to HDR
imagery (for example in the upcoming IIF profile).

Commits:
105dba932d32970d4cbb6d4fee77be99a18334a5
4b50d7b222538f637abd11fb03616e60ee2c73ab

Issue:
https://github.com/imageworks/OpenColorIO/issues#issue/11

-- Jeremy

No objections? Rolling it in...