When a file attachment has an updated revision in a pending draft, that

revision could leak into the page for users not able to see the draft.

If they then moved the revision slider to show the new revision, they'd

get a 404.
This change makes it so we check the last attachment in the history to

see if it's a draft, and only include it in the revision list if that

draft should be visible.

Ran unit tests.
Created a draft with an updated revision to a file. Saw that the owner

  saw two revisions, a regular user saw one, and admins saw either one

  or two depending on if they were choosing to view draft data.