A specialized local rearrange operator which behaves
like the regular local rearrange in the getNext()
as far as getting its input and constructing the
"key" out of the input. It then returns a tuple with
two fields - the key in the first position and the
"value" inside a bag in the second position. This output
format resembles the format out of a Package. This output
will feed to a foreach which expects this format.
Overridden since the attachment of the new input should cause the old
processing to end.
Calls getNext on the generate operator inside the nested
physical plan. Converts the generated tuple into the proper
format, i.e, (key,indexedTuple(value))