This required BL_ArmatureObject to have tighter control over armatures and poses.
Also, (Blender) armature objects are now copied instead of shared between
BL_ArmatureObjects to avoid race conditions. Also, due to the armature copy,
shape key drivers need a bit of extra fiddling to get the correct armature copy.
Initially OpenMP was used for threading, but then BLI_task was used due to being
less compiler dependent.
This commit also places time spent on skinning updates in the Animation
profiler category (was previously under the Rasterizer category).
fe05f97841