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 git://git.apache.org/pig into add_flatten_annotation