clear cache when erase is called

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1437325 13f79535-47bb-0310-9956-ffa450edef68
add some caching for userAssignement in LdapRbacManager

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1437326 13f79535-47bb-0310-9956-ffa450edef68