Propagate ignoreNodes to preconditioner

In analogy to a multigridstep and its basesolver/smoother/etc.

dune/solvers/iterationsteps/cgstep.cc

 // -*- tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 // vi: set et ts=8 sw=4 sts=4:
 
+#include <dune/solvers/common/canignore.hh>
+
 template <class MatrixType, class VectorType>
 void CGStep<MatrixType, VectorType>::check() const
 {
@@ -17,6 +19,11 @@ void CGStep<MatrixType, VectorType>::preprocess()
                 r_[i] = 0;
 
     if (preconditioner_) {
+        using CanIgnore_t = CanIgnore<DefaultBitVector_t<VectorType>>;
+        CanIgnore_t *asCanIgnore = dynamic_cast<CanIgnore_t*>(preconditioner_);
+        if (asCanIgnore != nullptr and this->hasIgnore())
+            asCanIgnore->setIgnore(this->ignore());
+
         preconditioner_->setMatrix(*matrix_);
         preconditioner_->apply(p_, r_);
     } else

dune/solvers/test/cgsteptest.cc

@@ -93,7 +93,6 @@ struct CGTestSuite
                                                   typename Problem::Vector>::
                     create(Dune::Solvers::BlockGS::LocalSolvers::gs(),
                            Dune::Solvers::BlockGS::Direction::SYMMETRIC);
-            blockgs.setIgnore(p.ignore);
             Dune::Solvers::CGStep<typename Problem::Matrix,
                                   typename Problem::Vector> cgStep(p.A, u_copy,
                                                                    rhs_copy,