msg/SimpleMessenger: remove duplicated interface docs

Document these in the interface, not the implementation; having two copies
clutters the header and invites them to get out of sync.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: fix obc leak on invalid LIST_SNAPS op

Signed-off-by: Sage Weil <sage@inktank.com>
common/RefCountedObject: take cct for debugging
osd: debug Session refs
debug refs on Connection
debug Pipe refs
debug message refs (incoming ones at least)