1. fixed a bug when cast float to string
2. delay result's cancelled time
3. update type check in CastTo
4. remove unused mysql channel log
5. update stop_be.sh, use kill -0 instead of flock -nx
6. update jprotobuf-rpc to 3.5.15 in Frontend, the previous version will cause too many threads in JVM
1. Implement Backend http server using libevent instead of mongoose.
2. Remove Old Hypertable rpc framework, use brpc instead.
3. Change rpc from FE to BE to brpc.
4. Fs broker support HDFS HA.
5. add more metrics to monitor.
6. Lots of bug fixed.
