[ticket/11696] Rename db_tools.php so it can be autoloaded

PHPBB3-11696
[ticket/11696] Remove manual loading of db_tools in extension controller test

Remember to store the file, before commiting it...

PHPBB3-11696
[ticket/11696] Rename constructor to __construct()

PHPBB3-11696
[ticket/11696] Move file to new directory

PHPBB3-11696
Merge pull request #1558 from nickvergessen/ticket/11696

[ticket/11696] Rename db_tools.php so it can be autoloaded