hdf5_ep

[svn-r5662] Purpose:
    Bug fix.

Description:
    The chunking code was using internal allocation routines to put blocks on
    a free list for reuse, instead of using the system allocation routines (ie.
    malloc, free, etc.).  This causes problems when user filters attempt to
    allocate/free chunks for their algorithm's use.

Solution:
    Switched the chunking code back to using the system allocation routines,
    we can address performance issues with them if it becomes a real problem.

Platforms tested:
    Linux 2.2.x (eirene) && IRIX64 6.5 (modi4)