message: Fixes for C++98 and clang compiler.
  Note: clang doesn't like the following in a gtest:
  EXPECT_EQ( AXOM_NULLPTR, ptr)
diff: @@ -143,7 +143,7 @@ public:
  }
  if(outputMeshVTK)
  {
  - std::ofstream mfem_stream(filename + ".vtk");
  + std::ofstream mfem_stream( std::string(filename + ".vtk").c_str() );
  m_mesh->PrintVTK(mfem_stream);
  }
  }
  @@ -620,7 +620,7 @@ public:
  // Create the MFEM mesh
  m_mesh = new mfem::Mesh(sstr);
  - EXPECT_NE(AXOM_NULLPTR, m_mesh);
  + EXPECT_TRUE(m_mesh != AXOM_NULLPTR);
  // Refine (and possibly jitter) the mesh several times
  for(int i=0 ; i< numRefine ; ++i)
  @@ -640,11 +640,11 @@ public:
  // Sanity checks on whether mesh is low or high order
  if(meshType == FLAT_MESH)
  {
  - EXPECT_EQ(AXOM_NULLPTR, m_mesh->GetNodes());
  + EXPECT_TRUE(m_mesh->GetNodes() == AXOM_NULLPTR);
  }
  else
  {
  - EXPECT_NE(AXOM_NULLPTR, m_mesh->GetNodes());
  + EXPECT_TRUE(m_mesh->GetNodes() != AXOM_NULLPTR);
  EXPECT_EQ(feCollName, m_mesh->GetNodalFESpace()->FEColl()->Name());
  }
  @@ -822,7 +822,7 @@ public:
  // Create the MFEM mesh instance
  m_mesh = new mfem::Mesh(sstr);
  - EXPECT_NE(AXOM_NULLPTR, m_mesh);
  + EXPECT_TRUE(m_mesh != AXOM_NULLPTR);
  // Refine (and possibly jitter) the mesh several times
  for(int i=0 ; i< numRefine ; ++i)
  @@ -842,11 +842,11 @@ public:
  // Sanity checks on whether mesh is low or high order
  if(meshType == FLAT_MESH)
  {
  - EXPECT_EQ(AXOM_NULLPTR, m_mesh->GetNodes());
  + EXPECT_TRUE(m_mesh->GetNodes() == AXOM_NULLPTR);
  }
  else
  {
  - EXPECT_NE(AXOM_NULLPTR, m_mesh->GetNodes());
  + EXPECT_TRUE(m_mesh->GetNodes() != AXOM_NULLPTR);
  EXPECT_EQ(feCollName, m_mesh->GetNodalFESpace()->FEColl()->Name());
  }
  