message: Use unique_ptr instead of raw pointer in DirectSubBlockSolver
diff: #include "../config/config.hpp"
  #include "densemat.hpp"
  #include "handle.hpp"
  +#include <memory>
  #ifdef MFEM_USE_MPI
  #include <mpi.h>
  @@ -895,14 +896,13 @@ class DirectSubBlockSolver : public Solver
  mutable Array<int> local_dofs;
  mutable Vector sub_rhs;
  mutable Vector sub_sol;
  - DenseMatrixInverse *block_solvers;
  + std::unique_ptr<DenseMatrixInverse[]> block_solvers;
  public:
  /// block_dof is a boolean matrix, block_dof(i, j) = 1 if j-th dof belongs to
  /// i-th block, block_dof(i, j) = 0 otherwise.
  DirectSubBlockSolver(const SparseMatrix& A, const SparseMatrix& block_dof);
  virtual void Mult(const Vector &x, Vector &y) const;
  virtual void SetOperator(const Operator &op) { }
  - virtual ~DirectSubBlockSolver() { delete [] block_solvers; }
  };
  /// Solver S such that I - A * S = (I - A * S1) * (I - A * S0).
  