rewrite address interpolation so that planet_osm_node is not needed

This allows address interpolations to work correctly when flatnode storage
is used for node coordinates.

To fix interpolations in an existing database, follow these steps:

  * invalidate all interpolations (in psql):
    `UPDATE placex SET indexed_status=2 WHERE rank_search = 28`
  * disable updates:
    ./utils/setup.php --create-functions --create-partition-functions
  * reindex the whole lot:
    ./utils/update.php --index --index-instances <number of your cpus>
  * enable updates again:
    ./utils/setup.php --create-functions --enable-diff-updates --create-partition-functions