Chunk server: fix replication and recovery with client threads by ensuring that the global variables are updated with the mutex held in replication / recovery completion handler, instead of replicator destructor, as the later can be invoked with no mutex acquired. Fix race with rs replicator ref. counter update with write completion and reader close completion by changing the ref. count with the mutex acquired. Fix write errors handling with RS replicator by initiating the reader close when returning from completion handler and "owner" op pointer set to 0.