Move the MultigridStep class into the Dune::Solvers namespace

... and import it back out, again.

dune/solvers/iterationsteps/multigridstep.hh

@@ -12,6 +12,10 @@
 
 #include "lineariterationstep.hh"
 
+namespace Dune {
+
+  namespace Solvers {
+
 /** \brief A linear multigrid step */
     template<
         class MatrixType,
@@ -228,6 +232,14 @@
         bool preprocessCalled;
     };
 
+  }   // namespace Solvers
+
+}   // namespace Dune
+
+
+// For backward compatibility: will be removed eventually
+using Dune::Solvers::MultigridStep;
+
 #include "multigridstep.cc"
 
 #endif