Lacunarity parameter determines scaling of subsequent octaves in fractal
noises. For example, Noise node have this scaling hardcoded to 2.0. Each
octave have twice bigger scale than previous one, resulting in finer details.
By design fractal noises that generate octaves with same seed should not
have Lacunarity set to 1.0, since then it just stacks up identical noises.
Differential Revision: https://developer.blender.org/D6742
842e71a1ef