PIG-3569: SUM function for BigDecimal and BigInteger (harichinnan via rohini)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1542017 13f79535-47bb-0310-9956-ffa450edef68
PIG-3568: Define the semantics of POStatus.STATUS_NULL (mwagner via cheolsoo)


git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1542432 13f79535-47bb-0310-9956-ffa450edef68
Merge latest trunk changes into tez branch


git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1542433 13f79535-47bb-0310-9956-ffa450edef68