[Ravan002]

Adding an EdwardsPoint and an AffinePoint with + never returns. The reference impls dereference both sides and call the by-value impl, and define_add_variants! forwards the by-value impl back to the reference one, so they call each other forever. += and - were fine because they go through to_edwards().

let g = EdwardsPoint::GENERATOR;
g + g.to_affine();      // before: hangs, after: g.double()
g.to_affine() + g;      // same

Both reference impls now convert the affine point with to_edwards(), like Sub and AddAssign already do. add_affine_point covers all four by-value and by-reference combinations; on master it hangs.