hdf5_ep

[svn-r3228] Purpose:
    Bug fixes
Description:
    Fix two bugs:
        - Datasets with vlen datatype which were created but not written to
            were not being read back in correctly from the file.
        - If an existing space conversion path was found for a conversion, it
            was possible that the optimized read/write routines would be used
            inappropriately.
Solution:
    Patched vlen datatype conversion code to correctly handle zero-length
    sequences.

    Added a check to the space conversion code to make certain that the
    optimized conversion routines are still appropriate when an existing
    path is found.
Platforms tested:
    FreeBSD 4.2 (hawkwind)