Meta server: fix authentication op handling in chunk server state machine, by ensuring that hello rcp is complete and no authentication rcp is in flight at the moment when the next chunk server rpc is about to be received.
Meta server: fix chunk write lease renew. Return chunk server and chunk access tokens to write master, except [redundant] tokens for the write master itself.
Chunk server: minor code cleanup, change message log level to error in unexpected op completion close.
Kfsio lib: implement ostream version of chunk server and chunk access tokens writer methods.
Meta server: implement chunk allocate response with chunk server and chunk access tokens. Implement chunk server and chunk access response caching with append allocations in the case if authenticated user id of the chunk allocation response matches.