vchoi_fork

[svn-r13067] Description:
    Add [quite] limited ability to update (ie. write) data for objects in
fractal heap.  Limited to just updating objects in managed heap blocks (i.e.
not 'tiny' or 'huge' objects) and must be updated with data of the same length
as the object in the heap.  Updating objects in compressed heaps does work
though [as long as the data isn't 'tiny' or 'huge'].
    Needed for changing the data value or the name of an attribute that is
stored in dense or shared storage.

Tested on:
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)