The "Update" functionality for file attachments was broken in several

ways. The most basic of these was an error that got introduced sometime

whereby we weren't plumbing the review request editor through into the

upload dialog, and so it couldn't create the new file attachment object.

This was an easy fix, but exposed other issues.
We used to reload the entire page after creating a new file attachment.

This was changed to send the form data via javascript, but that meant we

no longer reloaded the page, and so the new file attachment would be

appended to the list of file attachments and show up as a new one at the

end of the list, rather than replacing the old revision. I've fixed up

the review request editor to correctly manage its collection of file

attachment objects, and the editor view to add new file attachments at

the correct index (and remove thumbnails as they're removed from the

collection).

Updated various file attachments. Saw that drafts were created

  correctly and that the thumbnail at the correct index was reloaded.
Ran unit tests.