agent: Fix agent_public_key_from_file

[NIIBE Yutaka]

Hello,

I think that I reviewed recent reports (to gnupg-devel, to Debian BTS,
and to g10code BTS) and I've done what I can.

Then, may I ask to review mine?

On 12/25/2014 04:21 PM, NIIBE Yutaka wrote:
> Here is the part one of ECC key format fixes, fixing
> agent_public_key_from_file function.
[...]
> With this patch, KEYTOCARD works fine, and I believe no regression.

Well, I don't have concrete idea about the part two.  I don't know if
we should support arbitrary curves with parameters (for GnuPG).  I
think that OpenPGP specification for ECC requires OID to use (since
OID is a part of fingerprint calculation).  While we will add a curve
with OID in future, we will surly assign a name to that curve in
libgcrypt.
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