message: Option to use gslib or advection.
diff: // Compile with: make pmesh-optimizer
  //
  // Adaptive limiting:
  -// mpirun -np 4 pmesh-optimizer -m adaptivity_2.mesh -o 2 -rs 0 -mid 2 -tid 1 -ni 50 -ls 2 -bnd -qt 1 -qo 8 -vl 1 -al
  -// Adaptive limiting through FD:
  -// mpirun -np 4 pmesh-optimizer -m adaptivity_2.mesh -o 2 -rs 0 -mid 2 -tid 1 -ni 50 -ls 2 -bnd -qt 1 -qo 8 -vl 1 -al -fd
  +// mpirun -np 4 pmesh-optimizer -m adaptivity_2.mesh -o 2 -rs 0 -mid 2 -tid 1 -ni 50 -ls 2 -bnd -qt 1 -qo 8 -vl 1 -al -ae 0
  +// Adaptive limiting through FD (required GSLIB):
  +// * mpirun -np 4 pmesh-optimizer -m adaptivity_2.mesh -o 2 -rs 0 -mid 2 -tid 1 -ni 50 -ls 2 -bnd -qt 1 -qo 8 -vl 1 -al -fd -ae 1
  //
  // Sample runs:
  // Adapted analytic Hessian:
  @@ -285,6 +285,7 @@ int main (int argc, char *argv[])
  bool visualization = true;
  int verbosity_level = 0;
  bool fdscheme = false;
  + int adapt_eval = 0;
  bool adapt_lim = false;
  // 2. Parse command-line options.
  @@ -363,6 +364,8 @@ int main (int argc, char *argv[])
  "Enable or disable GLVis visualization.");
  args.AddOption(&verbosity_level, "-vl", "--verbosity-level",
  "Set the verbosity level - 0, 1, or 2.");
  + args.AddOption(&adapt_eval, "-ae", "--adaptivity evaluatior",
  + "0 - Advection based (DEFAULT), 1 - GSLIB.");
  args.Parse();
  if (!args.Good())
  {
  @@ -599,13 +602,13 @@ int main (int argc, char *argv[])
  // Adaptive limiting.
  ParGridFunction zeta_0(&ind_fes), zeta(&ind_fes);
  - ConstantCoefficient coeff_zeta(10.0);
  + ConstantCoefficient coef_zeta(10.0);
  if (adapt_lim)
  {
  FunctionCoefficient alim_coeff(adapt_lim_fun);
  zeta.ProjectCoefficient(alim_coeff);
  zeta_0.ProjectCoefficient(alim_coeff);
  - he_nlf_integ->EnableAdaptiveLimiting(zeta_0, zeta, coeff_zeta, 1);
  + he_nlf_integ->EnableAdaptiveLimiting(zeta_0, zeta, coef_zeta, adapt_eval);
  socketstream vis1;
  common::VisualizeField(vis1, "localhost", 19916, zeta_0, "Zeta 0",
  300, 600, 300, 300);
  