add a method to find user without using caching: jdo update need the object detach from database not a cached one

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1551098 13f79535-47bb-0310-9956-ffa450edef68
do not use cache when updating user

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1551101 13f79535-47bb-0310-9956-ffa450edef68