add/refresh functions from mapproxy to load datasources
removed duplicate code
fixed import
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
Merge branch 'master' into HEAD
RTree requires libspatialindex-dev