h4h5tools

Purpose:
   Fix bug
Description:
   Inside H4toh5 vdata conversion, I use H5Dopen to open the dataset twice without closing it;
the HDF5 1.6 will then generate a zero-length HDF5 file.
    [describe the bug, or describe the new feature, etc]
Solution:
    Add H5Dclose and the test passed.
    [details about the changes, algorithm, etc...]
    [Please as detail as you can since your own explanation is
    better than others guessing it from the code.]
Platforms tested:
I've tested on linux 2.4 and sol 2.7. Since I have to test both HDF5 and H4toH5; so I
think the two platforms are enough.
    [machines you have tested the changed version.  This is absolute
    important.  Test it out on at least two or three different platforms
    such as Big-endian-32bit (SUN/IRIX), little-endian-32(LINUX) and
    64-bit (IRIX64/UNICOS/DEC-ALPHA) would be good.]