Create applyDefaults() function that works similarly to extend(), but without replacing existing keys.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@111 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Util.js

@@ -604,3 +604,20 @@ OpenLayers.getParameterString = function(params) {
 OpenLayers.Util.getImagesLocation = function () {
     return "img/";
 };
+
+/** Takes a hash and copies any keys that don't exist from
+*   another hash, by analogy with Object.extend() from
+*   Prototype.js.
+*
+* @param {Object} to
+* @param {Object} from
+* @return {Object}
+*/
+OpenLayers.Util.applyDefaults = function (to, from) {
+    for (var key in from) {
+        if (to[key] == null) {
+            to[key] = from[key];
+        }
+    }
+    return to;
+};