Blender Git Loki

Cycles: change material output displacement to vector.

Previously only scalar displacement along the normal was supported,
now displacement can go in any direction. For backwards compatibility,
a Displacement node will be automatically inserted in existing files.

This will make it possible to support vector displacement maps in the
future. It's already possible to use them to some extent, but requires
a manual shader node setup. For tangent space maps the right tangent
may also not be available yet, depends on the map.

Differential Revision: https://developer.blender.org/D3015