osd: Only normalize extent if op uses extent

Code in ReplicatedPG was reading and modifying ceph_osd_op.extent,
even though that is a member of a union and only valid for some ops.

Signed-off-by: Adam Crume <adamcrume@gmail.com>
Give meaningful error when submodules are not checked out

Signed-off-by: Adam Crume <adamcrume@gmail.com>
Merge pull request #1978 from adamcrume/master

OSD bug fix and developer error message

Reviewed-by: Sage Weil <sage@redhat.com>