Change rss feed build name

With #2845 (released with Jenkins
2.58), if no display name is explicitly set the feed title contains only
the build number, which is not very useful for non project specific feeds
like the global /rssFailed feed.

This commit restores the old behaviour and honours the new behaviour of
pull request 2845.

core/src/main/java/hudson/model/Run.java

@@ -2422,7 +2422,10 @@ public final class KeepLogBuildBadge implements BuildBadgeAction {
 
     private static class DefaultFeedAdapter implements FeedAdapter<Run> {
         public String getEntryTitle(Run entry) {
-            return entry.getDisplayName()+" ("+entry.getBuildStatusSummary().message+")";
+            if (entry.hasCustomDisplayName()) {
+                return entry.getDisplayName()+" ("+entry.getBuildStatusSummary().message+")";
+            }
+            return entry+" ("+entry.getBuildStatusSummary().message+")";
         }
 
         public String getEntryUrl(Run entry) {