LensDistortOp bug and compatibility with negative formats.
Fixed a bug in the LensDistortOp where it has been applying the distortion upside down. Until now it has been unnoticable as the only lens model in Cortex is symmetrical in the Y axis.
Added support to the LensDistortOp for images with offset display window.
Added a test case for the LensDistort node in nuke.
The test case generates a set of test images and compares the output of the LensDistort node to that of the LensDistortOp.
Added an option to the ImageDiffOp that allows offset display windows of the same size to be aligned before comparison.
Merge pull request #171 from goddardl/ImageDiffOp

Extended the ImageDiffOp options.
Merge pull request #172 from goddardl/LensDistortOp

LensDistortOp bug and compatibility with negative formats.
IECoreNuke::LensDistort added a hash for the lens parameters.
Adding bounding box and point cloud options to SceneCache nodes
Replacing getRangeByValue with the most obvious implementation.

On a large asset (1500 shapes, 3 million polys), this improves loading time as follows for the following geometry types:

Cortex: 3.476s to 0.664s
Houdini: 8m 23s to 3m 20s
BoundingBox: 4.272s to 0.763s
PointCloud: 3.256s to 0.426s
Merge pull request #173 from andrewkaufman/geometryTypes

Houdini SceneCache Geometry Types