use requestAnimationFrame instead of setInterval for animations, when…

… available.

src/effects.js

@@ -363,7 +363,9 @@ jQuery.fx.prototype = {
 		t.elem = this.elem;
 
 		if ( t() && jQuery.timers.push(t) && !timerId ) {
-			timerId = setInterval(fx.tick, fx.interval);
+			jQuery.support.requestAnimationFrame ?
+				window[jQuery.support.requestAnimationFrame](fx.tick):
+				timerId = setInterval(fx.tick, fx.interval);
 		}
 	},
 
@@ -468,6 +470,8 @@ jQuery.extend( jQuery.fx, {
 
 		if ( !timers.length ) {
 			jQuery.fx.stop();
+		} else if ( jQuery.support.requestAnimationFrame ) {
+			window[jQuery.support.requestAnimationFrame](this);
 		}
 	},
 

src/support.js

@@ -58,6 +58,14 @@
 		// (WebKit defaults to false instead of true, IE too, if it's in an optgroup)
 		optSelected: opt.selected,
 
+		// Verify requestAnimationFrame mechanism existence
+		// use the prefixed name as the value
+		requestAnimationFrame: mozRequestAnimationFrame ?
+			'mozRequestAnimationFrame' :
+			webkitRequestAnimationFrame ?
+				'webkitRequestAnimationFrame' :
+				false,
+
 		// Will be defined later
 		deleteExpando: true,
 		optDisabled: false,