downloads: Inform user of duplicate version names

This information is included for hash-based lookups as well as
branch+shortrev-based since it's relevant in either case.

dolweb/downloads/templates/downloads-view-devrel.html

@@ -17,6 +17,18 @@ <h1>{% blocktrans with br=ver.revbranch %}Information for {{ br }}{% endblocktra
     data-ad-slot="5299890518"></ins>
 </div>
 
+{% if dupes }
+    {% for dupe in dupes %}{% with br=ver.revbranch hash=dupe.hash url=dupe.get_absolute_url %}
+        <p>{% blocktrans %}{{ br }} can also refer to <a href="{{ url }}">{{ hash }}</a>.{% endblocktrans %}</p>
+    {% endwith %}{% endfor %}
+
+    <p>{% blocktrans count num=dupes|length trimmed %}
+        Some or all of the download links below may be based on that version.
+        {% plural %}
+        Some or all of the download links below may be based on those versions.
+    {% endblocktrans %}</p>
+{% endif %}
+
 <div class="row">
     <div class="col-md-5">
         <dl>

dolweb/downloads/views.py

@@ -65,16 +65,20 @@ def buildlist(request):
 @render_to('downloads-view-devrel.html')
 def view_dev_release(request, hash):
     release = get_object_or_404(DevVersion, hash=hash)
+    releases = DevVersion.objects.filter(branch=release.branch,
+                                         shortrev=release.shortrev)
+    dupes = releases.exclude(hash=hash).order_by('date')
 
-    return { 'ver': release }
+    return { 'ver': release, 'dupes': dupes }
 
 @vary_on_headers('User-Agent')
 @render_to('downloads-view-devrel.html')
 def view_dev_release_by_name(request, branch, name):
     releases = get_list_or_404(DevVersion, branch=branch, shortrev=name)
     releases.sort(key=lambda ver: ver.date)
+    release, dupes = releases[0], releases[1:]
 
-    return { 'ver': releases[0] }
+    return { 'ver': release, 'dupes': dupes }
 
 @vary_on_headers('User-Agent')
 @render_to('downloads-view-release.html')