hdf5_ep

[svn-r5521] Purpose:
    Code improvement

Description:
    The metadata aggregation code in the library was not terribly smart about
    extending contiguous regions of metadata in the file and would not extend
    them as far as possible.  This causes space in the file to be wasted, also.

Solution:
    Be smarter about extending the space used in the file for metadata by
    checking whether new metadata blocks allocated in the file are at the end
    of the current metadata aggregation region and append them to the metadata
    region if so.  This has the nice side benefit of reducing the number of
    bytes we waste in the file and reducing the size of the file by a small
    amount in some cases.

    This reduces the number of I/O operations which hit the disk for my test
    program from 53 to 19 (i.e. from 393 to 19, overall).

Platforms tested:
    Solaris 2.7 (arabica) w/FORTRAN and FreeBSD 4.5 (sleipnir) w/C++