Better manage memory usage of condensediffs.

condensediffs had some memory issues. Even though we were using
QuerySet.iterator, it seems memory was still increasing far too much.

To work around this, we're using a couple tricks that we used in
loaddb and dumpdb. We're only operating on batches of 200 diffs at a
time, and are resetting queries and garbage-collecting after each batch.

The query resets shouldn't impact production installs, since DEBUG
should be False, but it's a precaution. We're also forcing DEBUG to be
False in the management command as well.

With these changes, memory still increases over time, to a degree, but
seems to stabilize. This is with a sample set of over 8200 diffs.

Reviewed at https://reviews.reviewboard.org/r/5870/
Improve the output of condensediffs.

condensediffs will now show a percentage of completion, making it easier
to see how much longer the operation will take. It also formats the
resulting byte counts with commas, for readability.

Reviewed at https://reviews.reviewboard.org/r/5871/
Fix bumping Last Updated on a review request when publishing a review.

We made a change to improve the performance of publishing a review by
limiting what fields we were writing on a ReviewRequest. However, we
weren't including "last_updated" in the list of fields, which meant that
a review request with a new review wouldn't jump to the top of the
dashboard. Adding that field to the list fixes this.

Fixes bug #3374
Reviewed at https://reviews.reviewboard.org/r/5875/
Spell check our documentation.

There were a bunch of small typos in the docs. I've gone through with ispell
and checked everything in docs/manual.

Reviewed at https://reviews.reviewboard.org/r/5873/
Fix typos and spelling in release notes.

I ran ispell on all our old release notes and fixed all the problems.

Reviewed at https://reviews.reviewboard.org/r/5874/
Merge branch 'release-2.0.x'