hdf5_ep

[svn-r5138] Purpose:
    Bug Fix & Code Cleanup

Description:
    The MPI-IO optimized transfer routines
    (H5S_mpio_spaces_read/H5S_mpio_space_write) are not being invoked in all
    the cases where they could be used.

    Additionally, the code for determining if an optimized transfer is wrapped
    into the actual I/O transfer routine in a very confusing way.

Solution:
    Re-enabled MPI-IO optimized transfer routines in all the cases where they
    should work.

    Extracted all the pre-conditions for optimized transfers into separate
    routines from the transfer routines.

Platforms tested:
    FreeBSD 4.5 (sleipnir) & IRIX64 6.5 (modi4)