- fixed bug in distance3D (intersects was called instead of intersect3D)
- changed exception type to InappropriateGeometryException in extrude
- fixed bug in isValid(Polygon)
- replaced SFCGAL_ASSERT_GEOMETRY_VALIDITY by
  SFCGAL_ASSERT_GEOMETRY_VALIDITY_2D in straight skeleton (since
projection in the xy plane invalidates 3D geom)
- added on formelly bugged case in DistanceTest
as a result, only one test fails in garden test, all test pass in unit
and regress/standalone