HIVE-4130 : Bring the Lead/Lag UDFs interface in line with Lead/Lag UDAFs (Harish Butani via Ashutosh Chauhan)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.11@1471682 13f79535-47bb-0310-9956-ffa450edef68