Added virtual destructor to reader and writer classes in order to avoid compiler warnings.

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@84 fdac6126-5c0c-442c-9429-916003d36597

Core/IO/reader/OFFReader.hh

@@ -101,6 +101,9 @@ public:
 
   _OFFReader_();
 
+  /// Destructor
+  virtual ~_OFFReader_() {};
+
   std::string get_description() const { return "Object File Format"; }
   std::string get_extensions()  const { return "off"; }
   std::string get_magic()       const { return "OFF"; }