OAK-928: Read access is enforced on NEW items

Add NodeBuilder.isReplaced() and use it to detect cases where a read-protected base state has been replaced with a fresh new one

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1544674 13f79535-47bb-0310-9956-ffa450edef68