Added tagging interface

[[Imported from SVN: r2736]]

common/interfaces.hh

@@ -8,12 +8,17 @@ namespace Dune {
   //! An interface class for cloneable objects
   struct Cloneable {
 
-    /** \brief ???
-       \todo Please doc me!!!
+    /** \brief Clones the object
+       clone needs to be redefined by an implementation class, with the
+       return type covariantly adapted. Remember to
+       delete the resulting pointer.
      */
     virtual Cloneable* clone() const = 0;
   };
 
+  //! Tagging interface to indicate that Grid provides typedef ObjectStreamType
+  struct HasObjectStream {};
+
 } // end namespace Dune
 
 #endif