Add compatibility with WP Geodirectory

WP Geodirectory does not create it’s meta fields / relationship fields in the standard WordPress way, so if you have two CPTs created by WP Geodirectory, you cannot create a “related things” section using the “Post Custom Field Contains Current Post ID” as if you enter, for example the default gd_place field as the custom field it does not show any posts – probably because a normal custom field does not exist with that name.