PG: simplify merge_log, remove old objects
PG: simplify merge_log, remove old objects

Previously, some old objects could escape removal during a log merge.
This patch also simplifies merge_log somewhat.

Signed-off-by: Samuel Just <4c46b94684b338bae1ed5e7e1321718dd75401cc@dreamhost.com>

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