Fix further issues with missing file attachments.

The previous fix for missing file attachments broke once the `f.close()`
call was moved into the `finally:` block if the file attachment was
missing, due to the fact that the initial statement failed and `f` was
not a valid variable. This change fixes this by creating two separate
`try/except` blocks.

It also sandboxes the generation of text-based file attachment comment
thumbnails, which would also break the page if the file was missing.

Reviewed at https://reviews.reviewboard.org/r/6444/
Merge branch 'release-2.0.x'
Fix some issues with the new file attachment display.

The new Update menu work for file attachments had a couple bugs that
prevented usage on new uploads, and broke tests.

Newly uploaded file attachments had an extra <li> tag, which broke the
tests and resulted in malformed HTML. They also didn't have a
functioning Update menu, since the menus were only ever created on
initial page render.

Existing file attachments had a stray "%}" in the class. This has
probably been there a while.

The menu could have been fixed with some more global menu registration
stuff, but it ended up getting messy. Instead, I've removed all the old
JS-level menu support, and simply moved it into CSS. Now, the browser
handles the display of menus for us. I also tweaked the animation time
to be a bit quicker and smoother.

To work around the issue of the Update menu sticking around on click
(which didn't work before, due to referencing a different class name,
and still didn't work here with that fixed), I've simply fixed the
z-orders so that the modal dialog overlay appears above the menu. The
menu is still on-screen until the mouse is moved away, but it's not
noticeable.

Reviewed at https://reviews.reviewboard.org/r/6445/
Prevent various inline editors from vertically shifting on open/close.

The inline editors in various places (replies to reviews/comments and in
the new review dialog) would shift a bit vertically when opening or
closing the editor. This was due to the pencil disappearing and the line
height shrinking where it used to be.

We had this solved for banners. Now, that solution is contained in a
macro, which is used in the other cases where we display these.

Reviewed at https://reviews.reviewboard.org/r/6446/
Prevent various inline editors from vertically shifting on open/close.

The inline editors in various places (replies to reviews/comments and in
the new review dialog) would shift a bit vertically when opening or
closing the editor. This was due to the pencil disappearing and the line
height shrinking where it used to be.

We had this solved for banners. Now, that solution is contained in a
macro, which is used in the other cases where we display these.

Reviewed at https://reviews.reviewboard.org/r/6446/
Merge branch 'release-2.0.x'
Fix all remaining JavaScript unit tests on master.

There were a couple other JavaScript unit tests that have been busted on
master. One had to do with bug links, and the other had to do with the
display of the branches in the New Review Request page. This fixes both.

Reviewed at https://reviews.reviewboard.org/r/6447/
Update the new review dialog for server-side Markdown.

The new server-side Markdown support was implemented on release-2.0.x,
and thus didn't take into account the new review dialog on master. This
dialog differed from the other places where Markdown was used, in that
we had no way to pre-inject the raw values for review and comment text
fields prior to loading the dialog.

Now, the dialog requests the raw text fields as part of the initial
fetches and the saves, and populates the raw values in the
inlineEditors. This allows the dialog to work as it did before, with the
addition of having server-side Markdown support.

Reviewed at https://reviews.reviewboard.org/r/6438/
Remove dead code from `diffReviewableview`

Remove some unused variables and computations from `DiffReviewableView`'s
`_updateCollapseButtonPos` method.

Reviewed at https://reviews.reviewboard.org/r/6455/
Merge branch 'release-2.0.x'