Hive hdfs

This is the pull request which integrates Abstract FS Writer with Hive.
Why is this field added to this operator when it doesn't need it? In your implementation you could cache it in beginWindow() and use it. The common implementations of FSWriter that we have seen so far  we do not need this. If you need it for your implementation you can create it there. The signature change that you have made to rotateHook is also not required.