PIG-3434: Null subexpression in bincond nullifies outer tuple (or bag)

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/branch-0.12@1527772 13f79535-47bb-0310-9956-ffa450edef68
PIG-3491: Fix e2e failure Jython_Diagnostics_4

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/branch-0.12@1527824 13f79535-47bb-0310-9956-ffa450edef68
Revert PIG-3471, 3457, 3464, and 3419


git-svn-id: https://svn.apache.org/repos/asf/pig/branches/branch-0.12@1527867 13f79535-47bb-0310-9956-ffa450edef68