OAK-2342: Clean up collision markers

Merged revision 1644479 from trunk (except for the oak-mongo.js changes, which doesn't exist in the branch).

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1644493 13f79535-47bb-0310-9956-ffa450edef68