hdf5_ep

[svn-r5542] Purpose:
    Code cleanup/bug fix

Description:
    Unused space in the file was being "dropped on the floor" when the metadata
    or "small data" block was moved to a new location in the file and there was
    unused space in the old block.

Solution:
    Put the space left in the allocation block into the free list of space for
    the file.  This allows it to be [potentially] reused and sometimes allows
    the file to be smaller.

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