agent: New option --enable-extended-key-format.
* agent/gpg-agent.c (oEnableExtendedKeyFormat): New const. (opts): New option --enable-extended-key-format. (parse_rereadable_options): Set option * agent/findkey.c (write_extended_private_key): Add arg 'update'. (agent_write_private_key): Implement new option.
- Signed-off-by: Werner Koch <wk@gnupg.org>