Fixed: WLForeignObjectByIdTransformer broken in recent revisions.

Before this fix, WLForeignObjectByIdTransformer only worked for objects with ids which had been seen before. If a new object was required, it was created but not returned by the transformer due to a bug in WLRemoteObject +instanceForPk:create:.

This fix restores WLRemoteObject +instanceForPk:create: functionality.