Pass correct result on dispute invalid post state root

[b-tarczynski]

It would be nice to emit RollbackTriggered with correct result when rollback is triggered by invalid post state root(right now it's Types.Result.Ok).

I added simple if statement in dispute functions, but I can change processCommit function for each batch type to accept additional postStateRoot as argument and return only Types.Result instead of postStateRoot and result. What do you think? @jacque006

[jacque006]

Definitely like this change, improves clarity of rollback reason in that case.

but I can change processCommit function for each batch type to accept additional postStateRoot as argument and return only Types.Result instead of postStateRoot and result.

^ I think this is the way to go to encapsulate the validation logic in process*Commit functions. However, I would double check the gas cost difference to make sure it doesn't change that significantly.

And finally, if it's feasible test cases for this new Result state would be appreciated :)

[b-tarczynski]

I changed process*Commit functions to be responsible for validation. Gas cost of disputeTransition* functions are the same as before changes.