osdc/Objecter: expose LingerOp instead of linger_id

We want a reference-counted handle, not an id.

Signed-off-by: Sage Weil <sage@redhat.com>
osdc/Objecter: spit out linger register step

Signed-off-by: Sage Weil <sage@redhat.com>
librados: use Objecter's linger_id as the cookie

Signed-off-by: Sage Weil <sage@redhat.com>
fix msg
osdc/Objecter: take Finisher ref from creator

Only needed for watch/notify users, so most can pass NULL.

Signed-off-by: Sage Weil <sage@redhat.com>
notify wip
wip