Modify usage of Inflate/deflate polygon in zone calculations, in order to be compatible with boost::polygon >= 1.56
Some code cleanup.
Modify usage of Inflate/deflate polygon in zone calculations, in order to be compatible with boost::polygon >= 1.56
 Inflate/deflate polygons does not work very well (neither with  boost::polygon >= 1.56 nor with Clipper) for polygons which have holes linked by overlapping segments
(i.e. polygons with holes which can be drawn, because they are see as only one polygon)
Some code cleanup.