HIVE-3984 : Maintain a clear separation between Windowing & PTF at the specification level.

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/ptf-windowing@1447989 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch 'remotes/apache_hive/ptf-windowing' into ptf