Fix MailContext mock in postage project further to new 2.5.0 version

git-svn-id: https://svn.apache.org/repos/asf/james/postage/trunk@1426731 13f79535-47bb-0310-9956-ffa450edef68
Fix compilation failure due to pom and new commons-configuration (POSTAGE-25)

git-svn-id: https://svn.apache.org/repos/asf/james/postage/trunk@1429302 13f79535-47bb-0310-9956-ffa450edef68