Update loader to support distribution of data on multiple instances.
'loadhdf' AFL function no longer writes directly to disk.  Instead it returns
a temporary array to its caller.  This allows us to wrap the load function in
a 'store()' operation which will take care of distributing data to multiple instances
with proper replication.  TODO:  now the 'loadhdf' operation is a blocking op...
it loads the data entirely into a temporary array before completion.  A more
efficient solution would be to implement it as a 'delegate' array and load the
data lazily as it is pulled by the 'store()' operator.