scd: add support for RSA_CRT and RSA_CRT_N key import.

* scd/app-openpgp.c (do_writekey): Added RSA_CRT and RSA_CRT_N support.

Updates of original patch by wk:

• unsigned char *rsa_u, *rsa_dp, rsa_dq; + unsigned char *rsa_u, *rsa_dp, *rsa_dq;

and AUTHORS. Missing signed-off-by assumed due to DCO send the other
day.