* src/gpgmetools.c (gpa_backup_key): Add arg is_x509 and support X.509
backups.
* src/gpabackupop.c (PROP_PROTOCOL): New.
(gpa_backup_operation_get_property): Add it.
(gpa_backup_operation_set_property): Add it.
(gpa_backup_operation_class_init): Install new property
(gpa_backup_operation_finalize): Remove surplus NULL check.
(gpa_backup_operation_do_backup): Pass x509 flag to gpa_backup_key.
(gpa_backup_operation_dialog_run): Add arg is_x509.  Move extra label
generation out of the static dialog generation.  Use ".p12" for X.509
keys.
(gpa_backup_operation_idle_cb): Pass x509 flag to the dialog run call.
(gpa_backup_operation_new): Create protocol property from KEY.
(gpa_backup_operation_new_from_fpr): Add arg protocol.
* src/gpabackupop.h (_GpaBackupOperation): Add field protocol.
* src/gpagenkeysimpleop.c (gpa_gen_key_simple_operation_done_cb): Pass
PROTOCOL to gpa_backup_operation_new_from_fpr.
* src/keymanager.c (key_manager_mapped): Assure that
gpa_backup_oepration_new is never called with a NULL key.