Preparing for release 0.12.0

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1525756 13f79535-47bb-0310-9956-ffa450edef68
Preparing for 0.13.0 development

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1525758 13f79535-47bb-0310-9956-ffa450edef68