fix #ifdef-conditions and document ALBERT_USES_MPI

[[Imported from SVN: r952]]

grid/albertgrid/agcommunicator.hh

 // -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 // vi: set et ts=4 sw=2 sts=2:
-#ifndef _DUNE_ALBERTGRID_COMMUNICATOR_HH_
-#define _DUNE_ALBERTGRID_COMMUNICATOR_HH_
+#ifndef DUNE_ALBERTGRID_COMMUNICATOR_HH
+#define DUNE_ALBERTGRID_COMMUNICATOR_HH
+
+// use this define to control if Albert should use the found MPI
+// #define ALBERT_USES_MPI 1
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
-#if !HAVE_MPI
-#undef ALBERT_USES_MPI
-#else
+#if defined(HAVE_MPI) && defined(ALBERT_USES_MPI)
 #include <mpi.h>
 #endif
 #endif
 
-
 #include <dune/common/dlist.hh>
 
 namespace Dune {
 
-#define COMMUNICATOR_COMM_TAG 457
+  static const int COMMUNICATOR_COMM_TAG = 457;
 
   /*!
      ProcListElement describes the link between two processors.
@@ -25,7 +25,7 @@ namespace Dune {
      these two procs.
    */
 
-#ifdef ALBERT_USES_MPI
+#if defined(HAVE_MPI) && defined(ALBERT_USES_MPI)
   template <class BufferType>
   class ProcListElement
   {
@@ -197,7 +197,7 @@ namespace Dune {
 
   };
 
-#ifdef ALBERT_USES_MPI
+#if defined(HAVE_MPI) && defined(ALBERT_USES_MPI)
   template <class GridType, class IndexSetType>
   class AlbertGridCommunicator
   {