HIVE-4081 [jira] allow expressions with over clause
(Harish Butani via Ashutosh Chauhan)

Summary:
fix lag amt less than part size issue; add wdw expr tests

remove current restriction where only a UDAF invocation is allowed with a windowing specification

Test Plan: included

Reviewers: JIRA, ashutoshc

Reviewed By: ashutoshc

CC: brock

Differential Revision: https://reviews.facebook.net/D9135

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/ptf-windowing@1453155 13f79535-47bb-0310-9956-ffa450edef68