Private key transfer format

[NIIBE Yutaka]

Hello,

I'm trying to fix the issue: https://bugs.g10code.com/gnupg/issue1937

Here, we need to enhance the OpenPGP Private Key Transfer Format.

Currently, as it is described in agent/keyformat.txt, it's like:

(openpgp-private-key
  (version V)
  (algo PUBKEYALGO)
  (curve CURVENAME)
  (skey _ P1 _ P2 _ P3 ... e PN)
  (csum n)
  (protection PROTTYPE PROTALGO IV S2KMODE S2KHASH S2KSALT S2KCOUNT))

For private keys in smartcard, it can be something like following:

(openpgp-private-key
  (version V)
  (algo PUBKEYALGO)
  (curve CURVENAME)
  (skey _ P1 _ P2 _ P3 ... _ PN_minus_1)  # ??? pkey???
  (csum n)
  (shadowed PROTOCOL (INFO)))

How about this?

If it's ok, it seems not good to say "skey" as it's public key
parameters only.  "pkey" would be better.

Besides, I found that the description of "ti-v1" (token info version 1).

In the current implementation, it is "t1-v1" (Tee-One Vee-One).  Shall we
support "ti-v1" too?  Or just fix the description in keyformat.txt?
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