PIG-3090: Introduce a syntax to be able to easily refer to the previously defined relation (jcoveney)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1437229 13f79535-47bb-0310-9956-ffa450edef68
PIG-3078: Make a UDF that, given a string, returns just the columns prefixed by that string (jcoveney)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1437235 13f79535-47bb-0310-9956-ffa450edef68
PIG-3091: Make schema, header and stats file configurable in JsonMetadata (pkommireddi via jcoveney)

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1437242 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of https://github.com/apache/pig into trunk