Hopefully, this will really clear up how the thing is supposed to work
(and that it's not SVP, nor MVTools).
I also removed instances of the word "interpolation", since that's a
term that's easily misleading.
Finally, I expanded on smoothmotion-threshold since the purpose/meaning
was a bit confusing.
(cherry picked from commit 9fa73b6f64)
Niklas Haas
220d28b902