map.getCenter() should return a cloned center, so that (for example)

transforming the center doesn't break the map. patch by edgemaster,
r=me, (Closes #1853)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@8410 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -1330,7 +1330,11 @@ OpenLayers.Map = OpenLayers.Class({
      * {<OpenLayers.LonLat>}
      */
     getCenter: function () {
-        return this.center;
+        var center = null;
+        if (this.center) {
+            center = this.center.clone();
+        }
+        return center;
     },