public boolean tryDelta(String string){
            int lastHash=hash;
            int lastState=state;
            delta(string);
            if (isValid()) return true;

            hash=lastHash;
            state=lastState;
            return false;
        }
Jumps ahead by string if that puts us into a valid state, does nothing otherwise

@return whether we jumped to a valid state (true) or di nothing (false)
fsa/src/main/java/com/yahoo/fsa/FSA.java