Just to confirm that this works correctly, because I broke it a few
times in different ways while working on T321121.
In this scenario, discussiontools_item_revisions contains rows for
the oldest and newest revisions of pages containing each comment
distinguishable by name, as well as extra rows for the newest
revisions of comments indistinguishable by name, so that they can
be looked up by ID.
Change-Id: Ic8450a6b082ed343dd633d3a43c50696b5d6d2bb