Fix KeyError: u'message' in SVN commits backend.

Not every commit we get has a message, which can cause exceptions to be thrown
from the repository commits resource. We already had one fix for this sort of
error with the author fields. This change fixes it up to do the same for
message and author everywhere.

Testing done:
Ran unit tests.

Addresses part of bug 3579.

Reviewed at https://reviews.reviewboard.org/r/6361/
Normalize the hooks_uuid field before saving the repository.

The hooks_uuid field would become a blank string after editing in the
admin UI. This resulted in a collision as soon as there was more than
one entry with a blank string.

We now normalize this to None if blank prior to saving.

Reviewed at https://reviews.reviewboard.org/r/6362/
Bullet-proof pre-commit UI a bit.

When receiving an unexpected error from the server, the frontend code for the
pre-commit upload would hit a TypeError, preventing it from completing the
process and leaving the browser with a forever "Loading..." message. This
change updates it to check when the response can't be parsed as JSON and show
"Unknown error" instead.

While I was in here I fixed up some of the nearby localization to be more
correct.

Testing done:
- Checked that uploading a diff through the pre-commit UI still worked as
  expected.
- Ran js-tests.

Reviewed at https://reviews.reviewboard.org/r/6365/
Fix the handling of binary data when reading in diff files in javascript.

Our drop-in replacement for File.readAsBinaryString wasn't entirely drop-in, in
that if it encountered any bytes > 127, it would fail with an
InvalidCharacterError, which would get translated into a fake ajax error that
said "HTTP 0" (which I don't have to tell you is completely useless). The
problem here was that we were using Int8Array instead of Uint8Array to convert
each byte into a String.

Testing done:
Made a diff that added a BOM to a utf-8 file. Tried to upload that diff and got
the same mysterious HTTP errors that appeared before any HTTP request got made.
After this change, the diff uploads correctly and I can see the added BOM in
the diff viewer.

Reviewed at https://reviews.reviewboard.org/r/6364/

Fixes bug 3579.
Add debugging and a script for issue count calculation.

There have been some reports of issue counts failing to calculate
correctly. The cause is not obvious, so we need better debugging.

This adds some debug logging to show all the calculation state for a
given review request's issues, which users can send us when they
encounter problems.

It also adds a reset-issue-counts management command, which will reset
issue counts for particular review requests, or all review requests if
passing --all.

Reviewed at https://reviews.reviewboard.org/r/6366/
Add help output for the rb-site manage command.

This includes some basic help output for rb-site's 'manage' command that
explains how to get the list of commands and execute them.

Reviewed at https://reviews.reviewboard.org/r/6367/
Add release notes for Review Board 2.0.8.

This covers all the fixes made since 2.0.7, and adds several new
contributors to the AUTHORS list.
Update the minimum versions of our dependencies.

This adds minimum versions of Haystack and Whoosh, in order to resolve
some version issues. It also updates the minimum versions of Djblets and
Django Evolution.
Release Review Board 2.0.8.
Bump to 2.0.9 dev.