Fix conflicts from ubuntu one

  After a couple of minutes, I got a lot of u1conflict files:
  photo.db
  photo.db.bak
  photo.db.u1conflict
  photo.db.u1conflict.1
  photo.db.u1conflict.2
  photo.db.u1conflict.3
  ...

  I guess the reason for this is that the photo.db from my laptop tried
  to be synced over to my server using Ubuntu One, while it was already
  updated by the Batware.

  This commit should prevent Batware from writing to the same file as
  shotwell.