[ticket/9871] Use $request->variable instead of request_var

PHPBB3-9871
[ticket/9871] Restore get_remote_file

PHPBB3-9871
[ticket/9871] Restore phpbb_version_compare

PHPBB3-9871
[ticket/9871] Mark test as slow

PHPBB3-9871
[ticket/9871] Typehint and comment on var types

PHPBB3-9871