only do article update operations once when scrolling

I discovered that DOM operations and function calls were done several times inside the 100px mirror when scrolling through articles. Especially painful on seamless scrolling systems like Mac OS, where dozens of updates would slow down this part dramatically. This change fixes it.

js/viewfeed.js

@@ -1281,7 +1281,8 @@ function headlines_scroll_handler(e) {
 				var child = rows[i];
 
 				if ($("headlines-frame").scrollTop < child.offsetTop &&
-					child.offsetTop - $("headlines-frame").scrollTop < 100) {
+					child.offsetTop - $("headlines-frame").scrollTop < 100 &&
+					child.id.replace("RROW-", "") != _active_article_id) {
 
 					if (_active_article_id) {
 						var row = $("RROW-" + _active_article_id);