OAK-1341 - DocumentNodeStore: Implement revision garbage collection (WIP)

Add method for batch removal to DocumentStore

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1582346 13f79535-47bb-0310-9956-ffa450edef68
OAK-1341 - DocumentNodeStore: Implement revision garbage collection (WIP)

Handle case where no checkpoint is created

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1582347 13f79535-47bb-0310-9956-ffa450edef68