Blender Git Loki

The OpenEXR include path needed to be a bit more elaborate... oddly
cmake always says OPENEXR_INC not found despite the fact that I have
the headers and it finds them correctly during building.

<digression>
There seems to be some conflict between setting, configuring as an
option, and autofinding files for some of the dependencies, and I don't
know how to resolve this.
</digression>