Fixed:correct the calculation of quorum in learner

Learner accumulates the vote when booth runs renew. 
the number of vote exceeds the total of acceptor after a little.
And then, booth always has the quorum.    

I consult the following wiki.
http://en.wikipedia.org/wiki/Paxos_%28computer_science%29

I think that booth implements renew() by using Multi-Paxos. However, booth still doesn't implement the instance number I(ref wiki). So, I add the instance number to paxos message. Learner can discerns a acceptor message in the same round. And, booth can calculate the correct vote number.