hdf5_ep

[svn-r7426] Purpose:
    Bug fix

Description:
    When datasets are deleted from a file, they are removed from the sieve
buffer, but instead of invalidating only the part of the sieve buffer affected,
the sieve buffer code would throw away the entire sieve buffer, potentially
including other raw data in the buffer that hadn't been written to disk yet.

Solution:
    Improve the sieve buffer clearing code to handle partial invalidations.

Platforms tested:
    FreeBSD 4.8 (sleipnir)
    h5committest