FLUME-1893. File Channel could miss possible checkpoint corruption.

(Hari Shreedharan via Mike Percy)
FLUME-2036. Make hostname optional for HTTPSource.

(Hari Shreedharan via Mike Percy)
FLUME-1981. Rpc client expiration can be done in a more thread-safe way.

(Hari Shreedharan via Mike Percy)
FLUME-1823. LoadBalancingRpcClient method must throw exception if it is called after close is called.

(Hari Shreedharan via Mike Percy)