Preparing for release 0.12.1

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/branch-0.12@1585023 13f79535-47bb-0310-9956-ffa450edef68
Preparing for release 0.12.1, committing KEYS

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/branch-0.12@1585258 13f79535-47bb-0310-9956-ffa450edef68