PIG-3908: Fix UnionOptimizer bug with expressions and MR compressions settings not honored (rohini)

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1589504 13f79535-47bb-0310-9956-ffa450edef68
PIG-3898: Refactor PPNL for non-MR execution engine (cheolsoo)


git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1589785 13f79535-47bb-0310-9956-ffa450edef68
PIG-3648-1