Merge pull request #1532 from ceph/wip-fast-dispatch

fast dispatch
This series adds an ms_fast_dispatch interface to the Messenger/Dispatcher, designed so that you can dispatch messages directly from the Pipe threads without going through the Dispatch queue.
It also sets the OSD to make use of this interface for most operations, and switches to finer-grained locking and use of local data in a bunch of different paths to enable that.

Reviewed-by: Samuel Just <sam.just@inktank.com>