Cycles: support for motion vector and UV passes.

Most of the changes are related to adding support for motion data throughout
the code. There's some code for actual camera/object motion blur raytracing
but it's unfinished (it badly slows down the raytracing kernel even when the
option is turned off), so that code it disabled still.

Motion vector export from Blender tries to avoid computing derived meshes
when the mesh does not have a deforming modifier, and it also won't store
motion vectors for every vertex if only the object or camera is moving.

intern/cycles/render/svm.h

@@ -69,7 +69,7 @@ public:
 	void add_node(const float4& f);
 	void add_array(float4 *f, int num);
 	uint attribute(ustring name);
-	uint attribute(Attribute::Standard std);
+	uint attribute(AttributeStandard std);
 	uint encode_uchar4(uint x, uint y = 0, uint z = 0, uint w = 0);
 	uint closure_mix_weight_offset() { return mix_weight_offset; }