Allows tests to set NODIFF

This gets set when the tests don't have a gold output, if they're too
big for example.
Add a DIV node

I guess Chisel still outputs DIV nodes.  I'm not sure exactly how I
missed this...
Add a rv32_1stage test case

Note that this Flo file had to be somewhat massaged in order to make
it work, as Chisel has been outputing a whole bunch of junk nodes.
Work around a Chisel bug

I have no idea where this is coming from, but it appears that Chisel
sometimes just outputs spurious MOV instructions.  In other words,
it'll emit something like:

  Tx = mov Ty

where neither "Tx" nor "Ty" appear anywhere else in the circuit.
While this seems like it's probably a serious Chisel bug, I'm just
going to straight-up ignore it because I don't want to deal with it
now.