Language download in ACP creates index.html and misses captcha_*

Language pack download on Board Administration -> System -> Language Pack screen creates index.html file in generated ZIP/TAR/GZ instead of index.htm which is expected by Titania translation system. This results in double index files in ZIP files downloaded from Titania. For more details see: http://www.phpbb.com/bugs/titania/ticket.php?ticket_id=62514

Also while at it, captcha_*.php files are not included in the downloaded ZIP file either.