message: Replace routines that will be deprecated in version 3.8
  add static qualifier to PetscErrorCode used within petsc.cpp
diff: @@ -122,7 +122,7 @@ typedef struct
  } __mfem_ts_ctx;
  // use global scope ierr to check PETSc errors inside mfem calls
  -PetscErrorCode ierr;
  +static PetscErrorCode ierr;
  using namespace std;
  @@ -1393,7 +1393,7 @@ void PetscSolver::SetMaxIter(int max_iter)
  else if (cid == TS_CLASSID)
  {
  TS ts = (TS)obj;
  - ierr = TSSetDuration(ts,max_iter,PETSC_DEFAULT);
  + ierr = TSSetMaxSteps(ts,max_iter);
  }
  else
  {
  @@ -1634,7 +1634,7 @@ int PetscSolver::GetNumIterations()
  {
  TS ts = (TS)obj;
  PetscInt its;
  - ierr = TSGetTotalSteps(ts,&its);
  + ierr = TSGetStepNumber(ts,&its);
  PCHKERRQ(ts,ierr);
  return its;
  }
  @@ -2838,7 +2838,7 @@ void PetscODESolver::Run(Vector &x, double &t, double &dt, double t_final)
  TS ts = (TS)obj;
  ierr = TSSetTime(ts, t); PCHKERRQ(ts, ierr);
  ierr = TSSetTimeStep(ts, dt); PCHKERRQ(ts, ierr);
  - ierr = TSSetDuration(ts, PETSC_DECIDE, t_final); PCHKERRQ(ts, ierr);
  + ierr = TSSetMaxTime(ts, t_final); PCHKERRQ(ts, ierr);
  ierr = TSSetExactFinalTime(ts, TS_EXACTFINALTIME_MATCHSTEP);
  PCHKERRQ(ts, ierr);
  