[maven-release-plugin] prepare release 2.6.4

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/branches/2.6@1530082 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/branches/2.6@1530084 13f79535-47bb-0310-9956-ffa450edef68