allow to give curve in Weierstrass form
Imported issue: Initially reported by @zimmerma in https://gforge.inria.fr/tracker/?group_id=135&aid=14883
Francois Morain suggests to allow to give the elliptic curve in Weierstrass form (at least for stage 2, since stage 1
requires Montgomery form, and conversion is not easy unless we know the factorization of N).
We could add arguments -wa A -wb B -wx0 X0 -wy0 Y0 for example.
Paul