The ssh-agent uses PKCS#11 to do its signing and handling of keys. The pkcs11/gkm/ code needs to have support for ECDSA added so that we can support it in the ssh-agent (the part that talks with clients) and ssh-store (the part that loads up ~/.ssh/).

 * Add support for converting ECDSA private keys to public in:
   - gkm_sexp_key_to_public()
 * Add tests for converting ECDSA private keys to public.
 * Add gkm-ecdsa-mechanism.[ch] similar to gkm-dsa-mechanism.[ch]. 
   - This includes the actual calls to libgcrypt to do the ECDSA signing
     and/or verify.
 * Implement returning the appropriate PKCS#11 attributes for ECDSA from
   the public and private key objects. At least the following functions need to
   be modified:
   - gkm_sexp_key_real_get_attribute()
   - gkm_public_xsa_key_real_get_attribute()
   - gkm_public_xsa_key_create_sexp()
   - gkm_private_xsa_key_real_get_attribute()
   - gkm_private_xsa_key_create_sexp()
 * Update gkm-module.c mechanism_list struct with information about the
   ECDSA mechanisms we support.
 * In gkm-data-der.[ch] add support for parsing private DER ECDSA keys, and
   public ECDSA keys as found in certificates.
   - This is used by the ssh-store to parse private keys from disk as well.
   - Add tests for parsing these private keys and certificates.
 * Add ECDSA to the appropriate switch statements and mappings in gkm-crypto.c.
   - These are used to call into gkm-ecdsa-mechanism.c functions