osd: clear waiting_for_head when we pull the head; set skipped if we do
osd: clear waiting_for_head when we pull the head; set skipped if we do

Need to ++skipped if we skip because we're waiting for the head
or else we'll incorrectly advanced requested_to.

Clear waiting_for_head entry when we pull a head we're waiting for.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph