OAK-2004 Add a way to pause the background async indexer
 - merged rev 1614891



git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1626194 13f79535-47bb-0310-9956-ffa450edef68
OAK-2088 AsyncIndexUpdate can leave orphaned checkpoint in case of abrupt shutdown
 - merged rev 1625620



git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1626195 13f79535-47bb-0310-9956-ffa450edef68
OAK-2104 - IndexStatsMBean should expose the time upto which the repository state has been indexed

Merging to 1.0 branch


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1626197 13f79535-47bb-0310-9956-ffa450edef68