Fix app linking with --disable-second

Now that we can optionally use the LaplacianErrorEstimator in the
calculator app, we need for the linker to be able to find its
constructor.

This should fix a failing devel->master build in the
`Test No Second Derivatives` recipe.

Author: roystgnr

src/error_estimation/fourth_error_estimators.C

@@ -17,28 +17,29 @@
 
 
 #include "libmesh/libmesh_config.h"
-#ifdef LIBMESH_ENABLE_SECOND_DERIVATIVES
 
+#include "libmesh/fourth_error_estimators.h"
 
-// C++ includes
-#include <algorithm> // for std::fill
-#include <cstdlib> // *must* precede <cmath> for proper std:abs() on PGI, Sun Studio CC
-#include <cmath>    // for sqrt
+#include "libmesh/enum_error_estimator_type.h"
 
+#ifdef LIBMESH_ENABLE_SECOND_DERIVATIVES
 
 // Local Includes
 #include "libmesh/libmesh_common.h"
-#include "libmesh/fourth_error_estimators.h"
 #include "libmesh/error_vector.h"
 #include "libmesh/fe_base.h"
 #include "libmesh/libmesh_logging.h"
 #include "libmesh/elem.h"
 #include "libmesh/system.h"
 #include "libmesh/dense_vector.h"
 #include "libmesh/tensor_tools.h"
-#include "libmesh/enum_error_estimator_type.h"
 #include "libmesh/enum_norm_type.h"
 
+// C++ includes
+#include <algorithm> // for std::fill
+#include <cstdlib> // *must* precede <cmath> for proper std:abs() on PGI, Sun Studio CC
+#include <cmath>    // for sqrt
+
 namespace libMesh
 {
 
@@ -157,28 +158,29 @@ LaplacianErrorEstimator::internal_side_integration ()
 
 #else // defined (LIBMESH_ENABLE_SECOND_DERIVATIVES)
 
-#include "libmesh/fourth_error_estimators.h"
-
 namespace libMesh
 {
 
-void
-LaplacianErrorEstimator::init_context (FEMContext &)
+LaplacianErrorEstimator::LaplacianErrorEstimator() :
+  JumpErrorEstimator()
 {
   libmesh_error_msg("Error: LaplacianErrorEstimator requires second " \
                     << "derivative support; try configuring libmesh with " \
                     << "--enable-second");
 }
 
-
-void
-LaplacianErrorEstimator::internal_side_integration ()
+ErrorEstimatorType
+LaplacianErrorEstimator::type() const
 {
-  libmesh_error_msg("Error: LaplacianErrorEstimator requires second "   \
-                    << "derivative support; try configuring libmesh with " \
-                    << "--enable-second");
+  return LAPLACIAN;
 }
 
+
+
+void LaplacianErrorEstimator::init_context (FEMContext &) {}
+
+void LaplacianErrorEstimator::internal_side_integration () {}
+
 } // namespace libMesh
 
 #endif // defined (LIBMESH_ENABLE_SECOND_DERIVATIVES)