Adaptive Cubic infill:

1) Fixed a wrong offset when extracting infill lines from the octree.
2) Added a variant for testing triangle in a bounding sphere
   when buildind the octree. Currently not used as the box test
   is more tight.
3) "Bridging infill" regions are now triangulated and used to densify
   the octree as well to support the bridging infill correctly.

src/libslic3r/Fill/FillAdaptive.hpp

@@ -40,7 +40,10 @@ Eigen::Quaterniond              transform_to_octree();
 
 FillAdaptive::OctreePtr         build_octree(
     // Mesh is rotated to the coordinate system of the octree.
-    const indexed_triangle_set  &triangle_mesh, 
+    const indexed_triangle_set  &triangle_mesh,
+    // Overhang triangles extracted from fill surfaces with stInternalBridge type, 
+    // rotated to the coordinate system of the octree.
+    const std::vector<Vec3d>    &overhang_triangles, 
     coordf_t                     line_spacing, 
     // If true, octree is densified below internal overhangs only.
     bool                         support_overhangs_only);