[parallelgrid] Implement InteriorBorder_InteriorBorder_Interface communication for elements as noop

dune/grid/parallelgrid/gridview.hh

@@ -211,6 +211,12 @@ namespace Dune
           break;
         }
       }
+
+      // currently we can only communicate elements and
+      // elements are never interior to two processes at the same time
+      else if (interface == InteriorBorder_InteriorBorder_Interface)
+          return;
+
       else
         DUNE_THROW( NotImplemented, "Communication on interface type " << interface << " not implemented." );
     }