Don't show duplicate builds in "Related builds"

Since a build may be a member of multiple jobset evaluations, we need
to do a "select distinct" here.  But maybe we should only show builds
from a single evaluation (e.g. the most recent), since showing builds
from several may be confusing.

src/root/build.tt

@@ -437,6 +437,7 @@
 	<div id="tabs-relatedbuilds">
 		
 		<h2>Related builds</h2>
+		<p>The following builds are part of the same jobset evaluation that produced this build.</p>
 		[% INCLUDE renderBuildList builds=relatedbuilds%]
 	</div>
         [% END %]