card: Improve openpgp key writing in "writecert".
* tools/card-keys.c (struct export_key_status_parm_s): New. (export_key_status_cb): New. (get_minimal_openpgp_key): New. * tools/gpg-card.c (cmd_writecert): Allow writing a keyblock directly from an existing gpg key.
- Signed-off-by: Werner Koch <wk@gnupg.org>