message: In mfem::mfem_backtrace, print addresses in hex format.
  In mfem::mfem_error, check both MPI_Initialized and MPI_Finalized before
  calling MPI_Abort.
diff: @@ -95,7 +95,7 @@ void mfem_backtrace(int mode, int depth)
  << (err ? 0 : info.dli_fbase);
  #endif
  }
  - std::cerr << " 0x" << addrs[i];
  + std::cerr << " 0x" << std::hex << addrs[i] << std::dec;
  }
  std::cerr << '\n';
  }
  @@ -120,9 +120,10 @@ void mfem_error(const char *msg)
  #endif
  #ifdef MFEM_USE_MPI
  - int flag;
  - MPI_Initialized(&flag);
  - if (flag) { MPI_Abort(MPI_COMM_WORLD, 1); }
  + int init_flag, fin_flag;
  + MPI_Initialized(&init_flag);
  + MPI_Finalized(&fin_flag);
  + if (init_flag && !fin_flag) { MPI_Abort(MPI_COMM_WORLD, 1); }
  #endif
  std::abort(); // force crash by calling abort
  }
  