[maven-release-plugin] prepare release apache-15

git-svn-id: https://svn.apache.org/repos/asf/maven/pom/trunk@1626895 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/maven/pom/trunk@1626897 13f79535-47bb-0310-9956-ffa450edef68