These two files place an extra int in the ug library when ug is built

with --enable-dune.  This allows the dune build system to check whether
ug has been built with that option.  This will be helpful because the
errors that result from forgetting --enable-dune are extremely
strange.

[[Imported from SVN: r8162]]

low/dunemarker.c

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+/****************************************************************************/
+/** \file
+    \brief Create a link time marker for the enable-dune build option.
+    \author Oliver Sander
+
+    If you want to use UG as part of DUNE, you have to build it with the
+    build-option --enable-dune.  However, this option affects header
+    files exclusively.  It is therefore impossible for the DUNE build
+    system to check whether UG has been built with this opion.  People
+    tend to forget it and then encounter strange errors.  To avoid this
+    we add a data field here which gets compiled into the UG library
+    if --enable-dune is set and can therefore be checked by the
+    DUNE build system.
+ */
+/****************************************************************************/
+
+
+/* RCS_ID
+   $Header$
+ */
+
+#include "namespace.h"
+#include "dunemarker.h"
+
+#ifdef FOR_DUNE
+/** \brief Data field which is only there for the DUNE build system to check
+    whether UG has been compiled with FOR_DUNE.
+ */
+int NS_PREFIX duneMarker = 0;
+#endif

low/dunemarker.h

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+/****************************************************************************/
+/** \file
+    \brief Create a link time marker for the enable-dune build option.
+    \author Oliver Sander
+
+    If you want to use UG as part of DUNE, you have to build it with the
+    build-option --enable-dune.  However, this option affects header
+    files exclusively.  It is therefore impossible for the DUNE build
+    system to check whether UG has been built with this opion.  People
+    tend to forget it and then encounter strange errors.  To avoid this
+    we add a data field here which gets compiled into the UG library
+    if --enable-dune is set and can therefore be checked by the
+    DUNE build system.
+ */
+/****************************************************************************/
+
+
+/* RCS_ID
+   $Header$
+ */
+
+#ifndef UG_DUNE_MARKER_H
+#define UG_DUNE_MARKER_H
+
+#include "namespace.h"
+
+START_UG_NAMESPACE
+
+/****************************************************************************/
+/*                                                                          */
+/* definition of exported global variables                                  */
+/*                                                                          */
+/****************************************************************************/
+
+#ifdef FOR_DUNE
+/** \brief Data field which is only there for the DUNE build system to check
+    whether UG has been compiled with FOR_DUNE.
+ */
+extern int duneMarker;
+#endif
+
+END_NAMESPACE
+
+#endif