Reject YAML violation witnesses

[sim642]

We can reject violation witnesses for programs that we can prove correct, assuming we are sound. This probably won't make us very good in the validation track though.

We could also consider actually interpreting the YAML violation witness and refining our analysis with that information. If there's no violation in the state space restricted by the violation witness and we can prove it, the witness is also invalid.

[sim642]

I guess we could also reject GraphML violation witnesses based on verdict, but it's probably kind of pointless. GraphML witnesses might become unused in SV-COMP sometime anyway.