vchoi_fork

[svn-r4723] Purpose:
    Bug fix (or more like feature)
Description:
    MPI_File_open does not truncate the filesize if file already exists.
    This created confusion during debugging as what the real file size
    is.  It also interfere the real write bandwidth since the times
    required to allocate new disk-space vanishes for subsequent writes
    that are for offset shorter than previous file sizes.
    Added a MPI_File_set_size to reset the file size to 0 for every new
    file.

    Another bug is that the 'remove()' call may not work for MPIO/PHDF5
    files. (e.g., filename may have some MPI prefix like "pfs:filename").
    Replaced "remove" with MPI_File_delete for those cases.
Platforms tested:
    modi4(pp) and eirene (pp)