don't log missing files for session bookmarks, as it's ok when documents don't have a file
don't log missing files for session bookmarks, as it's ok when documents don't have a file

git-svn-id: cb3fc60f0f557b927b8032d8a94e869b6f9f230b@6930 0fceea05-a30d-0410-8a8b-80ef821fb0a1

jasongrout/skim,jasongrout/skim