place=postcode places are artificial places that collect addr:postcode
points for aggration. They should neither show up in the address nor
be searchable. That means that there is no need to index them at all.
Only let boundary=postal_code through which define correct areas for
postcodes.
With ranks being dynamically changed through linking of places,
it is important to reset the ranks on update, so that changes
of the rank due to changes in linking are correctly taken into
account.
