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/writer/OFFWriter.hh

@@ -79,6 +79,8 @@ public:
 
   _OFFWriter_();
 
+  virtual ~_OFFWriter_() {};
+
   std::string get_description() const { return "no description"; }
   std::string get_extensions() const  { return "off"; }