vchoi_fork

[svn-r2990] Purpose:
    Bug fix (feature, kind of)
Description:
    The library used to hang if a collective dataset read/write request
    does not have the same number of eventual MPIO request.  Part of the
    reason is that H5FD_read/H5FD_write immediately returns succeess
    if it sees the request size is 0.  This caused problem since other
    processes with I/O to do would be hanging by waiting for the early
    returned process(es).
Solution:
H5FD.c: disable the early return code in parallel mode.  Make it
    go on even with "nothing" to transfer.
H5D.c: the optimized MPIO xfer routines can handle collect calls correctly
    when the condition is right (e.g., no conversion).  When the COLLECTIVE
    request cannot be handled correctly without the risk of hanging, the
    COLLECTIVE is changed to INDEPENDENT calls for the eventual MPIO
    calls.
Platforms tested:
    IRIX64 parallel (-64, n32), IRIX64 -64 sequential, Linux sequential.