Blender Git Loki

Reimplement curve smoothing in a clear way without premature optimizations.

The original code tries too hard to avoid allocating more memory, which
reduces clarity and is not necessary here as there aren't that many
f-curve keyframes in any case. Rewriting the code with a generic solver
somehow fixed the behavior of the curve in the totally unclamped case,
which suggests that there was a bug hidden in the optimizations.

In addition, the new solver allows treating the case when an Auto curve
segment ends at a Vector handle specially as a zero acceleration boundary
condition.