ReplicatedBackend: print char ack_type as int

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: make agent skip blocked obcs

Among other things, this can interfere with an in-flight copy-from and
corrupt the pg stats.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: improve whiteout debug prints

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