Fixes ILU for Dune 2.8

We got compile errors like:

/home/build/opm-simulators/opm/simulators/linalg/FlexibleSolver1.cpp:24:1:   required from here
/usr/include/dune/istl/ilu.hh:140:29: error: 'double' is not a class, struct, or union type

without this patch.
Hence we use the new internal ILU functions if available.

opm/simulators/linalg/FlexibleSolver_impl.hpp

@@ -21,9 +21,10 @@
 #ifndef OPM_FLEXIBLE_SOLVER_IMPL_HEADER_INCLUDED
 #define OPM_FLEXIBLE_SOLVER_IMPL_HEADER_INCLUDED
 
+#include <opm/simulators/linalg/matrixblock.hh>
+#include <opm/simulators/linalg/ilufirstelement.hh>
 #include <opm/simulators/linalg/FlexibleSolver.hpp>
 #include <opm/simulators/linalg/PreconditionerFactory.hpp>
-#include <opm/simulators/linalg/matrixblock.hh>
 
 #include <dune/common/fmatrix.hh>
 #include <dune/istl/bcrsmatrix.hh>

opm/simulators/linalg/ParallelOverlappingILU0.hpp

@@ -25,6 +25,7 @@
 #include <opm/common/ErrorMacros.hpp>
 #include <dune/common/version.hh>
 #include <dune/istl/preconditioner.hh>
+#include <dune/istl/ilu.hh>
 #include <dune/istl/paamg/smoother.hh>
 #include <dune/istl/paamg/graph.hh>
 #include <dune/istl/paamg/pinfo.hh>
@@ -430,7 +431,11 @@ namespace Opm
                                           detail::IsPositiveFunctor() );
             break;
         default:
+#if DUNE_VERSION_LT(DUNE_GRID, 2, 8)
             bilu0_decomposition( ILU );
+#else
+            Dune::ILU::blockILU0Decomposition( ILU );
+#endif
             break;
         }
     }
@@ -1022,7 +1027,11 @@ public:
                     break;
                 default:
                     if (interiorSize_ == A_->N())
+#if DUNE_VERSION_LT(DUNE_GRID, 2, 8)
                         bilu0_decomposition( *ILU );
+#else
+                        Dune::ILU::blockILU0Decomposition( *ILU );
+#endif
                     else
                         detail::ghost_last_bilu0_decomposition(*ILU, interiorSize_);
                     break;

tests/test_milu.cpp

@@ -85,7 +85,11 @@ void test_milu0(M& A)
 
     // Test that (LU)^-1Ae=e
     A.mv(e, x1);
+#if DUNE_VERSION_GTE(DUNE_ISTL, 2, 8)
+    Dune::ILU::blockILUBacksolve(ILU, x2, x1);
+#else
     bilu_backsolve(ILU, x2, x1);
+#endif
     diff = x2;
     diff -= e;