exit 2 means the run recorded a violation, and a predicate that throws
is recorded as one too. so was newAccountBalanceIsZero, an unrelated
property in the same spec. the gate read the exit code and went green
with detection dead.
web 3 and ios 7 convict 3 runs out of 3 with an exactly 2x witness.
android convicts 2 in 5 because the same seed does not walk the same
trajectory there, so it proves the app runs instead.
pj