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This is a new armature deform interpolation method using Dual Quaternions,
which reduces the artifacts of linear blend skinning:
http://www.blender.org/development/current-projects/changes-since-244/skinning/
Based on the paper and provided code:
Skinning with Dual Quaternions
Ladislav Kavan, Steven Collins, Jiri Zara, Carol O'Sullivan.
Symposium on Interactive 3D Graphics and Games, 2007.