[ticket/12384] Run Travis CI HHVM tests against MySQLi instead of MySQL.

HHVM MySQLi has been fixed and works for us now.

PHPBB3-12384
[ticket/12174] Update topic_attachment flag when a post is soft-deleted

https://tracker.phpbb.com/browse/PHPBB3-12174

PHPBB3-12174
[ticket/12174] Corrections

PHPBB3-12174
[ticket/12174] Revert the changes on $topic_update_array

PHPBB3-12174
[ticket/12174] Update sql query

PHPBB3-12174
[ticket/12174] Remove inline assignment

PHPBB3-12174
[ticket/12174] Update the conditions

PHPBB3-12174
[ticket/12174] Don't update the flag for a post without attachment

PHPBB3-12174
[ticket/12174] Remove $update_topic_attachments_flag

PHPBB3-12174
[ticket/12174] Coding style

PHPBB3-12174
[ticket/12527] Remove language file editor form ACP

PHPBB3-12527
[ticket/12527] Remove editor from template

PHPBB3-12527
[ticket/12527] Restore missing files and variables check

PHPBB3-12527
[ticket/12527] Check whether the language exists

PHPBB3-12527
[ticket/12527] Remove unnecessary language strings

PHPBB3-12527
[ticket/12527] Use a proper language string on confirm screen

PHPBB3-12527
[ticket/12536] Get Versions Should Not Require Both Stable and Unstable

https://tracker.phpbb.com/browse/PHPBB3-12536

PHPBB3-12536
[ticket/12536] Return empty array if stability unavailable

PHPBB3-12536
[ticket/12536] Update doc block

PHPBB3-12536
[ticket/12509] Add an option to set the path of custom file for extensions

https://tracker.phpbb.com/browse/PHPBB3-12509

PHPBB3-12509