Included missed language constant in checksum verification

lang/UTF-8/serendipity_lang_ru.inc.php

@@ -336,6 +336,7 @@ $i18n_filename_to   = array('_', 'a', 'A', 'b', 'B', 'v', 'V', 'g', 'G', 'd', 'D
 @define('SYNDICATION_PLUGIN_GENERIC_FEED', 'лента %s');
 @define('PERMISSIONS', 'Права доступа');
 @define('INTEGRITY', 'Verify Installation Integrity');
+@define('CHECKSUMS_NOT_FOUND', 'Unable to compare checksums! (No checksums.inc.php in main directory)');
 @define('CHECKSUMS_PASS', 'All required files verified.');
 @define('CHECKSUM_FAILED', '%s corrupt or modified: failed verification');
 @define('SETTINGS_SAVED_AT', 'Новые настройки были сохранены в %s');