gitweb: channel image in rss feed

Define the channel image for the rss feed when the logo or favicon are
defined, preferring the former to the latter. As suggested in the RSS
2.0 specifications, the image's title and link as set to the same as the
channel's.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -6075,6 +6075,16 @@ XML
 		      "<link>$alt_url</link>\n" .
 		      "<description>$descr</description>\n" .
 		      "<language>en</language>\n";
+		if (defined $logo || defined $favicon) {
+			# prefer the logo to the favicon, since RSS
+			# doesn't allow both
+			my $img = esc_url($logo || $favicon);
+			print "<image>\n" .
+			      "<url>$img</url>\n" .
+			      "<title>$title</title>\n" .
+			      "<link>$alt_url</link>\n" .
+			      "</image>\n";
+		}
 	} elsif ($format eq 'atom') {
 		print <<XML;
 <feed xmlns="http://www.w3.org/2005/Atom">