Supervisor modes

I changed operations so that it can be applied to replicated nodes, including bind, read, next, wait_needed, is_det, declare. There are still two operations 'fetch'  and 'reply_fetch' to be done. They are used to fetch values when a dataflow variable is bound to another.
What's the difference between ```test_set_next``` and ```set_next```.  Given nothing is documented, this is incredibly hard to follow.