[maven-release-plugin] prepare release STRUTS_2_3_12

git-svn-id: https://svn.apache.org/repos/asf/struts/struts2/trunk@1453277 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/struts/struts2/trunk@1453279 13f79535-47bb-0310-9956-ffa450edef68