Fix a breakage with saving repositories without hosting services.

The recent hosting service change broke saving repositories when
not using a hosting service. We're now more careful in what we check.
Release Review Board 1.7.8.1.
Fix the max_length of the new HostingServiceAccount.hosting_url.

A max_length of 256 doesn't work on MySQL with InnoDB. Instead, we need
to limit to 255.
Add the missing evolution for the hosting_url max_length change.
Fix references to cgit id=

id2= is actually for SHA-2 hashes, which standard git installations do
not provide.

See https://fedorahosted.org/fedora-infrastructure/ticket/3687 for
additional details.

Reviewed at http://reviews.reviewboard.org/r/3930/
Add blocks and depends_on fields to the Review Request resource.

The new support for the Depends On and Blocks fields didn't add any API
for getting these values to the Review Request resource. They've now
been added. Along with this, the documentation for the depends_on field
in the Review Request Draft resource has been fixed to point to the
right type.
Update the docs database for the latest schema changes.
Release Review Board 1.7.9.
Fix the Djblets version requirement.

The Djblets version requirement had both a == and <=, which confused
setuptools, leading to the new Djblets not being installed.

This fixes it to be a >=,<= in order to specify a proper range.

With this commit, we're also releasing a hotfixed Review Board 1.7.9.