PIG-3385: DISTINCT no longer uses custom partitioner

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1518039 13f79535-47bb-0310-9956-ffa450edef68
PIG-3435: Custom Partitioner not working with MultiQueryOptimizer

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1518040 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk
Merge remote branch 'origin/trunk' into trunk-gd