RB.CollectionView made an attempt to rebuild the list of views

whenever there was a sort event. There were some performance and DOM

update issues that came from this, and during the investigation, it

turned out that sort handling was often run unnecessarily.
collection.fetch(), by default, would prepare a list of models, add

them to the collection, sort them silently (avoiding any event

triggers), and then eventually trigger some events (including sort).

By the time RB.CollectionView saw the sort event, the models were

actually in the correct order, yet it would go through and rebuild the

views and re-add to the DOM.
This would have been harmless, but it actually broke <option selected>

children. On initial render, an <option selected> would normally

appear selected in the browser, but the sort would then happen

immediately after that render, and browsers wouldn't preserve the sort

order (tested with Chrome and Firefox).
This manifested as a bug in the New Review Request page's Branches

drop-down, where the last item would be selected despite the default

branch being marked as selected. It wasn't an issue in Review Board 3,

due to Backbone 1.0 only triggering this sort event if we were

actually intentionally sorting (the version we use in Review Board 4,

1.3.3, along with the latest version, 4.0, trigger it under more

conditions, including when populating an empty collection for the first

time without specifying reset: true as an option).
To avoid this, we're now comparing the order of stored views with the

new order. If it differs, we re-build the order of views and re-add to

the DOM. Otherwise, we skip the entire operation.
That not only fixes the <option selected> issue, but it also improves

performance.
There's one more performance improvement in this change, which is the

manner by which views are sorted and removed. We were looping through

the list of views, trying to find one with the proper model, and while

there was logic to reduce the search space, a more efficient approach is

just to keep a map of model IDs to views and use that for all lookup.
Combined, this change improves any views using RB.CollectionView and

avoids browser quirks.

All unit tests passed.
Tested the New Review Request page with a Mercurial repository. Saw that

the correct default branch was selected in the Branches list, instead of

the last branch in the list. Verified this on Chrome and Firefox.