Blender Git Loki

Added support for pixel-based density and Z depth information.

Availability of pixel-based density and Z depth information depends
on passes of a render layer being rendered.

- Density information is available if the diffuse pass of the render
layer is enabled. It is accessible through the DensityF0D and
DensityF1D functions provided by the Freestyle Python API. These
functions return 0 if the diffuse pass is disabled.

- Z depth information is available if the Z pass is enabled. It can
be accessed through LocalAverageDepthF0D and LocalAverageDepthF1D.
These functions return 0 if the Z pass is disabled.