[release,parallel] Suppress unused parameter warnings without DUNE_ISTL_WITH_CHECKING

dune/common/parallel/communicator.hh

@@ -1293,6 +1293,7 @@ namespace Dune
   template<class Data, class GatherScatter, bool FORWARD>
   inline void BufferedCommunicator::MessageGatherer<Data,GatherScatter,FORWARD,SizeOne>::operator()(const InterfaceMap& interfaces, const Data& data, Type* buffer, size_t bufferSize) const
   {
+    DUNE_UNUSED_PARAMETER(bufferSize);
     typedef typename InterfaceMap::const_iterator
     const_iterator;
     const const_iterator end = interfaces.end();