JCRVLT-64 Nodes that have a user parent are not installed if they are in the same .content.xml as their parent

- fixing case when installing content below a user that does not exist

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/commons/filevault/trunk@1636436 13f79535-47bb-0310-9956-ffa450edef68