OAK-1331: MicroKernel API: clarify semantics of  'read' method

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1567030 13f79535-47bb-0310-9956-ffa450edef68
OAK-1405 OR of different constraints broken

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1567031 13f79535-47bb-0310-9956-ffa450edef68