FLUME-2233. MemoryChannel lock contention on every put due to bytesRemaining Semaphore

(Hari Shreedharan via Roshan Naik)
FLUME-2231. Add details in Flume Ganglia config in User Guide

(Ashish Paliwal via Roshan Naik)
FLUME-2235. idleFuture should be cancelled at the start of append

(Hari Shreedharan via Jarek Jarcec Cecho)