MPI_Comm_free called twice?

[ykempf]

I was trying to run with TAU and got crashes in MPI_Comm_free with invalid communicator. I found two here:
https://github.com/fmihpc/vlsv/blob/master/vlsv_writer.cpp#L60 (destructor)
https://github.com/fmihpc/vlsv/blob/master/vlsv_writer.cpp#L196 (close())
and disabling the latter allows it to run.

What's better style? Dropping this one or the destructor one? Or should we dig deeper to make sure there's no other obscure issues involved?