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/secureware.c

@@ -106,7 +106,7 @@ sudo_secureware_cleanup(pw, auth)
     debug_decl(sudo_secureware_cleanup, SUDO_DEBUG_AUTH)
 
     if (pw_epasswd != NULL) {
-	zero_bytes(pw_epasswd, strlen(pw_epasswd));
+	memset_s(pw_epasswd, SUDO_CONV_REPL_MAX, 0, strlen(pw_epasswd));
 	efree(pw_epasswd);
     }
     debug_return_int(AUTH_SUCCESS);