improve dircache consistancy, enabled by MOOSEFS_DIR_CACHE
add default task status
bugfix
add outputLoc check before finish shuffle stage
fix retry with master conn
remove failed stage from pendingTasks
check outputLocs
Merge branch 'master' of http://github-ent.intra.douban.com/davies/dpark
fix risk condition with master connection
protect master connection by lock, retry when IOError
fix re-register to master after failover
fix bug in P2PBroadcast, wrong hostname.

delete object when clear broadcast
refactor
enable rdd cache: cached in disk (/dev/shm)
bugfix: cache non-iterator object in broadcast
add programing guide from @xiliang
Merge branch 'master' of github-ent.intra.douban.com:davies/dpark
Merge branch 'master' of github-ent.intra.douban.com:davies/dpark
Merge branch 'master' of http://github-ent.intra.douban.com/davies/dpark
typo