ecc: Fix key generation for a plain Ed25519 key.
* cipher/ecc.c (nist_generate_key): Use custom code for ED25519.
I wish there would a an RFC for Curve25519 - the description in the
paper is easy to misunderstand for a non-mathematician. Source code
and a paper are nice but a proper description (like those in the HAC)
would be better. Problem spotted by Florian Dold.
- Signed-off-by: Werner Koch <wk@gnupg.org>