PIG-3292: Logical plan invalid state: duplicate uid in schema during self-join to get cross product

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1528160 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk
Merge remote branch 'origin/trunk' into trunk-gd