Caching array length instead of accessing it with each iteration. r=crschmidt (closes #1636)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@7627 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Control/Attribution.js

@@ -75,7 +75,7 @@ OpenLayers.Control.Attribution =
     updateAttribution: function() {
         var attributions = [];
         if (this.map && this.map.layers) {
-            for(var i=0; i < this.map.layers.length; i++) {
+            for(var i=0, len=this.map.layers.length; i<len; i++) {
                 var layer = this.map.layers[i];
                 if (layer.attribution && layer.getVisibility()) {
                     attributions.push( layer.attribution );