gpg: New option --add-desig-revoker
* g10/gpg.c (oAddDesigRevoker): New. (opts): Add new option. * g10/options.h (opt): Add field desig_revokers. * g10/keygen.c (get_parameter_idx): New. (get_parameter): Make use of get_parameter_idx. (prepare_desig_revoker): New. (get_parameter_revkey): Add arg idx. (proc_parameter_file): Add designated revokers. (do_generate_keypair): Write all designated revokers.
(cherry picked from commit 3d094e2bcf6c9ed2cd405623f2dbc6131d04366f)
Support for v5 desig revokers has been removed. However, we should
check whether we can add a longer v4 desig revoker fingerprint in
addition to the regular v4 desig revoker.