use original conf directory and only shadow special files

_test/bootstrap.php

_test/conf/acl.auth.php

_test/conf/acronyms.conf

_test/conf/dokuwiki.php

_test/conf/entities.conf

_test/conf/interwiki.conf

_test/conf/license.php

_test/conf/local.php

_test/conf/local.php.dist

_test/conf/mediameta.php

_test/conf/mime.conf

_test/conf/mysql.conf.php.example

_test/conf/plugins.php

_test/conf/plugins.required.php

_test/conf/scheme.conf

_test/conf/smileys.conf

_test/conf/users.auth.php

_test/conf/wordblock.conf

_test/core/TestUtils.php