Add secp256k1 curve.

* cipher/ecc-curves.c (curve_aliases): Add secp256k1 and its OID.
(domain_parms): Add secp256k1's domain paramerter.

* tests/basic.c (check_pubkey): Add a key of secp256k1.

* tests/curves.c (N_CURVES): Updated.

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The key in check_pubkey is from "Test vector 1" of following page.
    https://en.bitcoin.it/wiki/BIP_0032_TestVectors

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
Fix assembly division check

* configure.ac (gcry_cv_gcc_as_const_division_ok): Correct variable
name mismatch at '--Wa,--divide' workaround check.
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Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>