PIG-3420: Failed to retrieve map values from data loaded by AvroStorage (yuanlid via rohini)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1514523 13f79535-47bb-0310-9956-ffa450edef68
PIG-3422: AvroStorage failed to read paths separated by commas (yuanlid via rohini)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1514537 13f79535-47bb-0310-9956-ffa450edef68