only fix generalized polygons by buffering, but not linestrings
new BoundaryPolygons mapping class that keeps inserted ways
improve load performance of large limit-to geometries
handle shapely errors when creating clipped limit-to geometries
update invalid polygons with additional mapping
Merge branch 'master' of https://github.com/olt/imposm into update_invalid_geoms

Conflicts:
	imposm/db/postgis.py
add example to default_mapping for validationtables
fixed missing polygon parts in limit-to intersections
refactored polygon validation
Merge branch 'master' into update_invalid_geoms