Code review comment for lp://staging/~julian-edwards/launchpad/dsp-changelog-bug-419147

= Summary =
Add DistributionSourcePackage:+changelog

== Proposed fix ==
The current DSP page has a change log section at the bottom. As part of the
3.0 redesign, this is being moved to a separate page. This branch adds that
page ahead of the redesign.

== Implementation details ==
Note that the new page is not linked to yet, that will only happen in the
final redesign. When I land that branch, I will amend the XXX in the changed
test in this branch so it follows the link.

Otherwise, this is a pretty trivial change.

== Tests ==
bin/test -vvt xx-distribution-packages.txt

== Demo and Q/A ==
https://launchpad.dev/ubuntu/+source/alsa-utils/+changelog

= Launchpad lint =

Checking for conflicts. and issues in doctests and templates.
Running jslint, xmllint, pyflakes, and pylint.
Using normal rules.

Linting changed files:
  lib/lp/registry/browser/configure.zcml
  lib/lp/registry/browser/distributionsourcepackage.py
  lib/lp/registry/stories/distribution/xx-distribution-packages.txt