This prevents the safety oracle from mistakenly finalizing in the cases where blocks that come after in sequence of a latest block in the justification of another latest block disagree with the estimate. The following diagram shows an example of this: (omitted)
The turan oracle is a type of clique oracle and one of the more conservative (and quick to execute) safety oracles. This should do for checking safety of blocks in Node v0.3. Note since disagreements have not been implemented there may be false positives on safety. A follow up PR implementing disagreements will come soon.