minor improvement: adding @Override, removing unused imports and replacing Session.checkPermission by Session.hasPermission

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/trunk@1640530 13f79535-47bb-0310-9956-ffa450edef68
JCR-3830 : Allow for privilege discovery in jcr-server

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/trunk@1640531 13f79535-47bb-0310-9956-ffa450edef68