* sm/gpgsm.c (oAssertSigner, oNoop): New.
(opts): Add option --assert-signer.
(assert_signer_true): New var.
(main): Set new option.
(gpgsm_exit): Handle assert_signer_true.
* sm/gpgsm.h (opt): Add field assert_signer_list.
* sm/verify.c (is_x509_fingerprint): New.
(check_assert_signer_list): New.
(gpgsm_verify): Handle option.