Fixed some cracks in the fill surfaces created by rounding all surfaces inside detect_surface_type().
Fixed https://github.com/prusa3d/Slic3r/issues/12
Bridging-Angle not optimal
Extended the "Ensure veritcal wall thickness" mode (merged with the original discover_horizontal_shells function), but this a work in progress. Already Slic3r with "ensure vertical wall thickness" produces less spurious infills inside solids.
