increase splitting for large geometries

increase splitting for large geometries

When computing the address parts for a geometry, we need to do
a ST_Relates lookup in the location_area_large_* tables. This is
potentially very expensive for geometries with many vertices.
There is already a funtion for splitting large areas to reduce the
impact. This commit reduces the minimum area of a split, effectively
increasing the number of splits.

The effect on database size is minimal (around 3% increase), while
the indexing speed for streets increases by a good 60%.