Clarify the error messages in 08f6ae5b

Ensure it is clear to the user why there has been an error.
Reviewed-by: NRich Salz <rsalz@openssl.org>

apps/cms.c

@@ -413,8 +413,8 @@ int cms_main(int argc, char **argv)
             break;
         case OPT_SECRETKEY:
             if (secret_key != NULL) {
-                /* Cannot be supplied twice */
-                BIO_printf(bio_err, "Invalid key %s\n", opt_arg());
+                BIO_printf(bio_err, "Invalid key (supplied twice) %s\n",
+                           opt_arg());
                 goto opthelp;
             }
             secret_key = OPENSSL_hexstr2buf(opt_arg(), &ltmp);
@@ -426,8 +426,8 @@ int cms_main(int argc, char **argv)
             break;
         case OPT_SECRETKEYID:
             if (secret_keyid != NULL) {
-                /* Cannot be supplied twice */
-                BIO_printf(bio_err, "Invalid id %s\n", opt_arg());
+                BIO_printf(bio_err, "Invalid id (supplied twice) %s\n",
+                           opt_arg());
                 goto opthelp;
             }
             secret_keyid = OPENSSL_hexstr2buf(opt_arg(), &ltmp);
@@ -442,8 +442,8 @@ int cms_main(int argc, char **argv)
             break;
         case OPT_ECONTENT_TYPE:
             if (econtent_type != NULL) {
-                /* Cannot be supplied twice */
-                BIO_printf(bio_err, "Invalid OID %s\n", opt_arg());
+                BIO_printf(bio_err, "Invalid OID (supplied twice) %s\n",
+                           opt_arg());
                 goto opthelp;
             }
             econtent_type = OBJ_txt2obj(opt_arg(), 0);

apps/req.c

@@ -296,7 +296,7 @@ int req_main(int argc, char **argv)
             break;
         case OPT_SET_SERIAL:
             if (serial != NULL) {
-                /* Cannot be supplied twice */
+                BIO_printf(bio_err, "Serial number supplied twice\n");
                 goto opthelp;
             }
             serial = s2i_ASN1_INTEGER(NULL, opt_arg());

apps/x509.c

@@ -262,7 +262,7 @@ int x509_main(int argc, char **argv)
             break;
         case OPT_SET_SERIAL:
             if (sno != NULL) {
-                /* Cannot be supplied twice */
+                BIO_printf(bio_err, "Serial number supplied twice\n");
                 goto opthelp;
             }
             if ((sno = s2i_ASN1_INTEGER(NULL, opt_arg())) == NULL)