Merge some BS1.7 changes:

Boolean operation feature

src/slic3r/GUI/MeshUtils.hpp

@@ -150,7 +150,8 @@ public:
         Vec3f& position, // where to save the positibon of the hit (mesh coords)
         Vec3f& normal, // normal of the triangle that was hit
         const ClippingPlane* clipping_plane = nullptr, // clipping plane (if active)
-        size_t* facet_idx = nullptr // index of the facet hit
+        size_t* facet_idx = nullptr, // index of the facet hit
+        bool sinking_limit = true
     ) const;
 
     // Given a vector of points in woorld coordinates, this returns vector