more postal code for cities

For cities with "Municipal Arrondissement" (admin level 9) we take the postal code of
them and affect a range to the corresponding city.

And we now get the postcode of the "admin_centre" too.

This changes will have to be ported in osm2ed...
You have a prettier rtree in boost: http://www.boost.org/doc/libs/1_56_0/libs/geometry/doc/html/geometry/spatial_indexes.html (this RTree interface is just sooo C89 ;))