Close #636. Support `ms` as well as `m` as time precision when querying
Protect protobuf client from simultaneous calls to reconnect()

Thanks to @freeformz for noticing this bug. Previously reconnect()
acquired a lock on entry, but that didn't protect us from a situation
where reconnect() is called twice in a row. The first time, a new
connection will be established but the second call will disconnect this
connection and open a new one. This can cause unexpected results since
the request sent on the first connection may not get a chance to receive
a response before the second call to reconnect() closes the connection.
Fix #637. Truncate log file if the last request wasn't written properly
Update the changelog
Fix #640. Update cluster config to track the last used shard id and increment for new ones
Merge pull request #646 from influxdb/fix-640-duplicate-shard-ids

Fix #640. Update cluster config to track the last used shard id and incr...
Update CHANGELOG.md
Update CHANGELOG.md
Update CHANGELOG.md
add statistic json api
fix travis build
use RWMutex