gpg: New option --default-new-key-algo.

* common/openpgp-oid.c (openpgp_is_curve_supported): Add optional arg
R_ALGO and change all callers.
* common/util.h (GPG_ERR_UNKNOWN_FLAG): New error code.
* g10/options.h (struct opt): Add field DEF_NEW_KEY_ALGO.
* g10/gpg.c (oDefaultNewKeyAlgo): New enum.
(opts): New option "--default-new-key-algo".
(main): Set the option.
* g10/keygen.c: Remove DEFAULT_STD_ FUTURE_STD_ constants and replace
them by ...
(DEFAULT_STD_KEY_PARAM, FUTURE_STD_KEY_PARAM): new string constants.
(get_keysize_range): Remove arg R_DEF and return that value instead.
Change all callers.
(gen_rsa): Use get_keysize_range instead of the removed
DEFAULT_STD_KEYSIZE.
(parse_key_parameter_part): New function.
(parse_key_parameter_string): New function.
(quick_generate_keypair): Refactor using parse_key_parameter_string.
(generate_keypair): Ditto.
(parse_algo_usage_expire): Ditto.
--

This new option is intended to be used in the forthcoming
--set-profile command of gpgconf.  It allows to provide a gpg
configuration with custom defaults for a new key using the simple
commands which use the default algorithm set.

Signed-off-by: Werner Koch <wk@gnupg.org>

g10/options.h

@@ -120,6 +120,8 @@ struct
   const char *agent_program;
   const char *dirmngr_program;
 
+  const char *def_new_key_algo;
+
   /* Options to be passed to the gpg-agent */
   session_env_t session_env;
   char *lc_ctype;