OAK-1114: Clarify NodeBuilder.moveTo() contract
- Adapted NodeBuilder.moveTo contract to cater for edge cases
- Updated test expectations accordingly
- Added Javadoc to MemoryNodeBuilder

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1544516 13f79535-47bb-0310-9956-ffa450edef68