MIssed fill_size change.
Added intercepts to modify mutator modifying object

This is an easier an more reliable way to ensure a the repl_reduced
mutator was actually called rather than the message passing one.
Made read_repair interaction tests more reliable

Using the new repl_reduced mutator interactps that modify an object,
it is far easier to tell if an object has been put through the
mutators properly. It also doesn't rely on internal workings of
read-reapir to ensure it passes/works either.