Bugfix of bottom bridges. If close regions shall be closed by bridges,

these regions are grown to anchor the bridge lines to the bottom surface.
The grown regions may overlap. In that case the regions are now merged
before the bridging direction is calculated for the merged region.

xs/src/libslic3r/SurfaceCollection.hpp

@@ -30,6 +30,9 @@ class SurfaceCollection
     void filter_by_type(SurfaceType type, Polygons* polygons);
     void append(const SurfaceCollection &coll);
     void append(const SurfaceType surfaceType, const Slic3r::ExPolygons &expoly);
+
+    // For debugging purposes:
+    void export_to_svg(const char *path, bool show_labels);
 };
 
 }