Implement memset_s() and use it instead of zero_bytes().

A new constant, SUDO_CONV_REPL_MAX, is defined by the plugin
API as the max conversation reply length.  This constant can be
used as a max value for memset_s() when clearing passwords
filled in by the conversation function.

plugins/sudoers/auth/sudo_auth.c

@@ -254,7 +254,7 @@ verify_user(struct passwd *pw, char *prompt, int validated)
 		goto done;
 	}
 	if (!standalone)
-	    zero_bytes(p, strlen(p));
+	    memset_s(p, SUDO_CONV_REPL_MAX, 0, strlen(p));
 	pass_warn();
     }