0024023: Revamp the OCCT Handle - gcc and clang

Adaptations for compiling with GCC 4.7 and 4.8:
- Construction semantics is used for Handle objects being initialized by const Handle objects of derived type, to avoid overload resolution error in GCC 4.7.
- Missing includes added.
- Fixed bugs related to misuse of direct casts of handle.
- Eliminate CLang warnings on uninitialized and unused variables, functions, and expressions

src/BRepOffsetAPI/BRepOffsetAPI_MiddlePath.cxx

@@ -978,7 +978,7 @@ void BRepOffsetAPI_MiddlePath::Build()
       {
         cout<<endl<<"Interpolation failed"<<endl;
       }
-      Handle(Geom_Curve) InterCurve = Interpol.Curve();
+      Handle(Geom_Curve) InterCurve (Interpol.Curve());
       MidEdges(i) = BRepLib_MakeEdge(InterCurve);
       i = j;
     }