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
Merge remote branch 'origin/trunk' into trunk
Merge remote branch 'origin/trunk' into trunk-gd