scd: Track the currently selected app.
* scd/scdaemon.h (struct server_control_s): Add 'current_apptype'. * scd/command.c (scd_clear_current_app): New. * scd/app.c (app_new_register): Set it. (deallocate_card): Clear it.
- Signed-off-by: Werner Koch <wk@gnupg.org>