AcRxObject：很少被覆盖的函数

自定义类很少重写这些函数：

virtual AcRxObject*       
clone() const;
 
virtual Acad::ErrorStatus
copyFrom(const AcRxObject* pSrc);
 
// Do not override; AcDbObject behavior is already accounted for.
//
virtual HRESULT __stdcall 
QueryInterface ( REFIID riid, 
                 void ** ppvObject );
 
virtual ULONG __stdcall 
AddRef();
 
virtual ULONG __stdcall 
Release();