hugae arg modexp (>512 bytes)

[letypequividelespoubelles]

in some ref tests, we get this failure:

"Final Scenario hasn't been set":
[
"idPrecomps_d4g0v0_London[London]",
"modexp_d28g0v0_London[London]",
"modexp_d29g0v0_London[London]",

This happens at commit time. The issue is that we shouldn't reach commit time for those tests, as we're calling MODEXP with more than 512 bytes arg, so the transaction should be popped. But as we don't have the pop mechanism for reference tests, we try to trace those transactions, and it fails.