为地图添加logo连接

var mapnik = new OpenLayers.Layer.TMS(

                "OpenStreetMap (Mapnik)",

                  "http://a.tile.openstreetmap.org/",

                {

                    type: 'png', getURL: osm_getTileURL,

                    displayOutsideMaxExtent: true,

                    attribution: '<a href="http://www.openstreetmap.org/">OpenStreetMap</a>'

                }

            );
map.addLayers([mapnik  ,start, stop,result]);