Fix diffFragmentQueueView js-tests.

The _addScript method is now called with a callback, but we were just testing
the arguments without it. Because it's hard to use
expect().toHaveBeenCalledWith(), I've switched it to introspect the
mostRecentCall. Trivial change.

Testing done:
Ran js-tests.
Don't save every comment when publishing from the "Edit Review" dialog.

The code that calculated whether or not we needed to save the comment models in
the "Edit Review" dialog was saving every comment, because we never fetched the
original extra data (which meant that it was comparing the extra data object
against undefined). This change adds some code to actually assign
`this._origExtraData`, which fixes the issue.

Testing done:
- Ran js-tests
- Added some instrumentation and checked that when I had modified (but not
  saved) a comment, it would save it as part of the publish operation, but if I
  hadn't modified it, or if I'd modified and saved it, it would skip that and
  only save the review.

Reviewed at https://reviews.reviewboard.org/r/6518/
Minor documentation change to webapi resource model (File attachment/Screenshot comment)

1. /reviewboard/webapi/resources/file_attachment_comment.py: typo "filess"

2. /reviewboard/webapi/resources/review_file_attachment_comment.py: file
   attachment comments do not contain dimension infomation, while screenshot
   comments do have.

3. /reviewboard/webapi/resources/screenshot_comment.py: apparently these should
   be comments on a screenshot.

Testing Done:
No testing required.

Reviewed at https://reviews.reviewboard.org/r/6528/
Merge branch 'release-2.0.x'