Load selected feed after a short timeout

Avoid firing multiple server requests if the user is navigating up/down
the tree list with the keyboard. Instead, wait till the user has stopped
navigating for at least 250ms.

js/feedlist.js

@@ -2,6 +2,7 @@ var _infscroll_disable = 0;
 var _infscroll_request_sent = 0;
 var _search_query = false;
 var _viewfeed_last = 0;
+var _viewfeed_timeout = false;
 
 var counters_last_request = 0;
 
@@ -52,7 +53,7 @@ function loadMoreHeadlines() {
 }
 
 
-function viewfeed(feed, method, is_cat, offset, background, infscroll_req) {
+function viewfeed(feed, method, is_cat, offset, background, infscroll_req, can_wait) {
 	try {
 		if (is_cat == undefined)
 			is_cat = false;
@@ -132,15 +133,24 @@ function viewfeed(feed, method, is_cat, offset, background, infscroll_req) {
 
 		console.log(query);
 
+		if (can_wait && _viewfeed_timeout) {
+			setFeedExpandoIcon(getActiveFeedId(), activeFeedIsCat(), 'images/blank_icon.gif');
+			clearTimeout(_viewfeed_timeout);
+		}
+
 		setActiveFeedId(feed, is_cat);
 
-		new Ajax.Request("backend.php", {
-			parameters: query,
-			onComplete: function(transport) {
-				setFeedExpandoIcon(feed, is_cat, 'images/blank_icon.gif');
-				headlines_callback2(transport, offset, background, infscroll_req);
-				PluginHost.run(PluginHost.HOOK_FEED_LOADED, [feed, is_cat]);
-			} });
+		timeout_ms = can_wait ? 250 : 0;
+		_viewfeed_timeout = setTimeout(function() {
+
+			new Ajax.Request("backend.php", {
+				parameters: query,
+				onComplete: function(transport) {
+					setFeedExpandoIcon(feed, is_cat, 'images/blank_icon.gif');
+					headlines_callback2(transport, offset, background, infscroll_req);
+					PluginHost.run(PluginHost.HOOK_FEED_LOADED, [feed, is_cat]);
+				} });
+		}, timeout_ms); // Wait 250ms
 
 	} catch (e) {
 		exception_error("viewfeed", e);

js/tt-rss.js

@@ -272,13 +272,13 @@ function init() {
 				var rv = dijit.byId("feedTree").getNextFeed(
 						getActiveFeedId(), activeFeedIsCat());
 
-				if (rv) viewfeed(rv[0], '', rv[1]);
+				if (rv) viewfeed(rv[0], '', rv[1], null, null, null, true);
 		};
 		hotkey_actions["prev_feed"] = function() {
 				var rv = dijit.byId("feedTree").getPreviousFeed(
 						getActiveFeedId(), activeFeedIsCat());
 
-				if (rv) viewfeed(rv[0], '', rv[1]);
+				if (rv) viewfeed(rv[0], '', rv[1], null, null, null, true);
 		};
 		hotkey_actions["next_article"] = function() {
 				moveToPost('next');