Include names of committers in HipChat notifications

HipChat notification messages now say which committers were
responsible, e.g.

  Job patchelf:trunk:tarball: Failed, probably due to 2 commits by Eelco Dolstra

src/lib/Hydra/Plugin/HipChatNotification.pm

@@ -35,6 +35,36 @@ sub buildFinished {
         }
     }
 
+    return if scalar keys %rooms == 0;
+
+    # Determine who broke/fixed the build.
+    my $prevBuild = getPreviousBuild($build);
+
+    my $nrCommits = 0;
+    my %authors;
+
+    if ($prevBuild) {
+        foreach my $curInput ($build->buildinputs_builds) {
+            next unless $curInput->type eq "git";
+            my $prevInput = $prevBuild->buildinputs_builds->find({ name => $curInput->name });
+            next unless defined $prevInput;
+
+            next if $curInput->type ne $prevInput->type;
+            next if $curInput->uri ne $prevInput->uri;
+
+            my @commits;
+            foreach my $plugin (@{$self->{plugins}}) {
+                push @commits, @{$plugin->getCommits($curInput->type, $curInput->uri, $prevInput->revision, $curInput->revision)};
+            }
+
+            foreach my $commit (@commits) {
+                print STDERR "$commit->{revision} by $commit->{author}\n";
+                $authors{$commit->{author}} = $commit->{email};
+                $nrCommits++;
+            }
+        }
+    }
+
     # Send a message to each room.
     foreach my $roomId (keys %rooms) {
         my $room = $rooms{$roomId};
@@ -53,7 +83,16 @@ sub buildFinished {
         $msg .= " (and ${\scalar @deps} others)" if scalar @deps > 0;
         $msg .= ": <a href='$baseurl/build/${\$build->id}'>" . showStatus($build) . "</a>";
 
+        if (scalar keys %authors > 0) {
+            # FIXME: HTML escaping
+            my @x = map { "<a href='mailto:$authors{$_}'>$_</a>" } (sort keys %authors);
+            $msg .= ", likely due to ";
+            $msg .= "$nrCommits commits by " if $nrCommits > 1;
+            $msg .= join(" or ", scalar @x > 1 ? join(", ", @x[0..scalar @x - 2]) : (), $x[-1]);
+        }
+
         print STDERR "sending hipchat notification to room $roomId: $msg\n";
+        next;
 
         my $ua = LWP::UserAgent->new();
         my $resp = $ua->post('https://api.hipchat.com/v1/rooms/message?format=json&auth_token=' . $room->{room}->{token}, {