scd:p15: Show a pretty PIN prompt.
* scd/app-p15.c (struct prkdf_object_s): New fields common_name and serial_number. (release_prkdflist): Free them. (keygrip_from_prkdf): Parse cert and set them. (any_control_or_space): New. (make_pin_prompt): New. (verify_pin): Construct a pretty PIN prompt. (do_sign): Remove debug output.
The D-Trust card has the SerialNumber part of the Subject printed on
the front matter, we assume this is also possible with other cards and
thus we show this as serial number.
The holder of the card is also extracted from the card's subject.
- Signed-off-by: Werner Koch <wk@gnupg.org>