Unfortunately there was nobody to rescue me. So I hacked my way out of it. First I changed the php settings so I would see the errors.
First error
Cannot redeclare class wp_import in ../wp-admin/import/wordpress.php on line 3
Solution: modified line 83 of wp-admin/admin.php.
from:
include(ABSPATH . "wp-admin/import/$importer.php");
to:
include_once(ABSPATH . "wp-admin/import/$importer.php");
Second error
Fatal error: Cannot redeclare write_post() (previously declared in ../wp-admin/admin-functions.php:4) in ..//wp-admin/admin-functions.php on line 3
Solution: changed lines 5 and 6 from “wp-admin/upgrade-functions.php”
from:
require_once(ABSPATH . '/wp-admin/admin-functions.php');
require_once(ABSPATH . '/wp-admin/admin-db.php');
to:
require_once(ABSPATH . 'wp-admin/admin-functions.php');
require_once(ABSPATH . 'wp-admin/admin-db.php');
Now it works. You won’t see the normal WordPress admin interface but only the import page. Ugly but you won’t use it often anyway. I may be advisable to undo the changes after importing to make sure nothing gets broken.