DXT: include mpiio offset
The MPI-IO entries to the DXT file don't have any offset information. This pull request fixes that with calls to
These routines in ROMIO turn "counts of file types" into "bytes" by walking the flattened type description. In some really hairy cases (E3SM comes to mind) this could take a bit of time. ROMIO is going to go do the same type-walking internally so probably not adding a lot of overhead to an already challenging workload, but I wanted to point out that these routines are more costly than say 'fseek(fd, 0, SEEK_POS)'