added IsDofManager for loadBalance in ALUGrid.

[[Imported from SVN: r4586]]

common/interfaces.hh

@@ -49,6 +49,9 @@ namespace Dune {
         DefaultImp>::ObjectStreamType ObjectStreamType;
   };
 
+  //! Tagging interface to indicate that class is of Type DofManager
+  struct IsDofManager {};
+
 } // end namespace Dune
 
 #endif