change of semantics of `hornerE`

[affeldt-aist]

https://github.com/math-comp/trajectories/blob/1b0221af1baac5e2253788c80ad8bac7b1585c86/theories/casteljau.v#L594-L598

If I am not mistaken, hornerE has changed with last MathComp releases, this part might need to be updated but this is a minor issue.

[ybertot]

I think we should give up backward compatibility to versions of math-comp that existed before the semantic change. I do have a fix that is backward compatible, but that gives code that will be awkward to read in the long run.

[affeldt-aist]

You are right.

[ybertot]

fixed by #34