osd: debug Session refs

Signed-off-by: Sage Weil <sage@inktank.com>
msg: debug Connection refs

Signed-off-by: Sage Weil <sage@inktank.com>
msg/Pipe: debug Pipe refs

Signed-off-by: Sage Weil <sage@inktank.com>
msg/Message: use RefCountedObject ctor to set initial ref count

Also, drop the useless assert in the dtor (the RefCountedObject dtor does
the same).

Signed-off-by: Sage Weil <sage@inktank.com>
common/RefCountedObject: make nref, cct private

Signed-off-by: Sage Weil <sage@inktank.com>
msg: debug refs on incoming Messages

Signed-off-by: Sage Weil <sage@inktank.com>