0025571: Avoid base Classes without virtual Destructors

Destructors of collection classes from NCollection and math_Function are made virtual to allow safe destruction by pointer to base class.

Destructors of classes HatchGen_IntersectionPoint, IntCurveSurface_Intersection, Intf_Interference, IntRes2d_Intersection are made protected to avoid possibility of destructing by pointer to corresponding base class.

src/Intf/Intf_Interference.hxx

@@ -90,9 +90,12 @@ public:
 
 protected:
 
-  
+  //! Empty constructor
   Standard_EXPORT Intf_Interference(const Standard_Boolean Self);
   
+  //! Destructor is protected, for safer inheritance
+  ~Intf_Interference () {}
+
   //! Only one argument for the intersection.
   Standard_EXPORT void SelfInterference (const Standard_Boolean Self);