JOSM validation: self-intersecting ways

[roelderickx]

After converting a shapefile to osm the JOSM validator may report self-intersecting ways among other errors and warnings.

Reordering nodes is not enough to solve this specific warning. In stead the ways should be split up on every intersection point, which may require extra nodes to be added. As a result there will be a number of new circular ways, if the original way is circular and part of a relation then the role (inner or outer) of all new ways must be recalculated. This will potentially degrade the performance significantly, and it should be noted that not all use-cases of ogr2osm require this.