Disable ORDER BY way "clustering"

[pnorman]

Testing indicates that a modified pinning number is no better with
ORDER BY way than by clustered/ordered on osm_id. As the table at
this point are approximately ordered by ID, skip ordering completely.

The modified pinning number is the pinning number, but instead of a
point, an area equivalent to a rendering meta-tile.

For high zooms and a true pinning number ordering by ID is effective,
probably because typically the ways right around a point were created
at about the same time.

For low zooms, a clustering on gist (way) may be desirable, but this
is something the user will have to consider, particularly as it takes
a decent amount of time to do this clustering, and significantly
increases the disk space requirements during the import process.

Benchmarks show the pinning number is within 10% for both a full planet and an extract and the ID-ordered z12 modified pinning number is 50% of the ORDER BY way z12 modified pinning number for the line table and 90% for the polygon table.

@apmon, I know there's some conflicts between this and the threading branch, but this also completely eliminates a section you had to change, making the merge simpler.

[pnorman]

CLUSTER on the gist indexes is still potentially worth it. I don't believe we should cluster by default. I looked at other tools that load geodata into a postgis database (ogr2ogr, imposm) and they don't CLUSTER by default, only if a flag is specified on the command line.

[apmon]

I have a patch in the threading branch that allows to select via command line option if and how to cluster by geometry.

[pnorman]

closing - we need to refactor this part to provide options for how to "cluster", and this would need rebasing against C++