The might_have_unfound set is used by the primary OSD during recovery.
This set tracks the OSDs which might have unfound objects that the
primary OSD needs. As we receive Missing from each OSD in
might_have_unfound, we will remove the OSD from the set.
When might_have_unfound is empty, we will mark objects as LOST if the
latest version of the object resided on an OSD marked as lost.
Signed-off-by: Colin McCabe <colinm@hq.newdream.net>