OAK-780 Revision.fromString() only parses two counter digits - changed revision id format

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1470512 13f79535-47bb-0310-9956-ffa450edef68
OAK-781: Clarify / fix effects of MISSING_NODE as base state of NodeBuilder

Better documentation about NodeBuilder, especially the new exists() method

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1470513 13f79535-47bb-0310-9956-ffa450edef68