Fixed Window.onerror type signature.

https://developer.mozilla.org/en/DOM/window.onerror
http://msdn.microsoft.com/en-us/library/cc197053(v=VS.85).aspx

std/js/Dom.hx

@@ -628,6 +628,7 @@ typedef Window = {
 	var onresize : Event -> Void;
 	var onscroll : Event -> Void;
 	var onunload : Event -> Void;
-	var onerror : Event -> Void;
+
+	var onerror : String -> String -> Int -> Bool;
 
 }