OpenMPI 1.2.5 and earlier do not let you set the Errhandler for
MPI::FILE_NULL using the C++ bindings.
[You would want to do so because, on error, MPI::File::Open() and
MPI::File::Delete() call the Errhandler associated with FILE_NULL.]
With the C++ bindings, MPI::FILE_NULL is a const object, and Set_errhandler
is apparently a non-const function -- so compiling fails.
MPI::Errhandler oldeh = MPI::FILE_NULL.Get_errhandler();