Davies Liu: cache direntry in masterconn

reduce thread context switch to hold consistant

add cache info in master first, then add data in client,
remove data in client, then remove cache info in master
Davies Liu: fix bug in concurrent condition
Davies Liu: use getattr (cached) instead of opencheck when readonly
Davies Liu: no opencheck when create with readonly
Davies Liu: do not cache dir in 10 seconds after invalidate it.

invalidate dir cache after notify attr 10 times
Davies Liu: merge slow writes into larger one by every seconds.

delay first write by 1 second. cancel the delay when flush or end.
Davies Liu: skip blank line when parsing topology.cfg
Davies Liu: NoAtime: do not update atime and reduce ACCESS in changelog

merge patch from Travis Hein <marsairforce@gmail.com>
Davies Liu: do not report space when all changes < 0.5%