Add malicious solver (verification game test)

[hswick]

I was able to mess up the scrypt-interactive client during the verification game by randomly submitting wrong/correct responses which would make the verifier fail by changing the order of steps being queried.

I don't think we have this problem, however it would be nice to have this scenario as a test.

[teutsch]

Interesting; good idea. The bug is that the scrypt-interactive doesn't always perform a binary search?

[hswick]

Yeah, basically.