PIG-3585: Make union work with Tez (cheolsoo)


git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1546867 13f79535-47bb-0310-9956-ffa450edef68
Remove comments that are no longer applicable in PigProcessor


git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1546868 13f79535-47bb-0310-9956-ffa450edef68