Change the nonreg test scheme by inverting the role of v4 and v6 in the sut and the oracle.

The rationale is to avoid local vars blow-up on some
examples. Indeed, the generated oracle blows-up (e.g., on left.lus)
if we execute it via v4, whereas via v6 it works fine.

This change triggers a couple of bugs that ware easy to fix
(confusion between div and slash) that I've fixed along the way.
For the others, I'll see later.

Overall it's a progress albeit
  #fail: 80 -> 83

indeed:
  #unresolved: 20 -> 12
  #passes		878 -> 883
  time: 335 -> 228