add displayProjection API Property on the Map, and on relevant controls.

Spherical mercator example now makes use of this, displaying coordinates 
in lon/lat instead of meters, and permalink/argparser now work in lon/lat
as well. this functionality will make using SphericalMercator easier for
a number of applications. 
r=tschaub (Closes #1036)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@5519 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

examples/spherical-mercator.html

@@ -25,7 +25,8 @@
 
         function init(){
             var options = {
-                projection: "EPSG:900913",
+                projection: new OpenLayers.Projection("EPSG:900913"),
+                displayProjection: new OpenLayers.Projection("EPSG:4326"),
                 units: "m",
                 maxResolution: 156543.0339,
                 maxExtent: new OpenLayers.Bounds(-20037508, -20037508,
@@ -104,6 +105,8 @@
                            yahoo, yahoosat, yahoohyb, mapnik, wms, vector]);
             map.addControl(new OpenLayers.Control.LayerSwitcher());
             map.addControl(new OpenLayers.Control.EditingToolbar(vector));
+            map.addControl(new OpenLayers.Control.Permalink());
+            map.addControl(new OpenLayers.Control.MousePosition());
             map.zoomToMaxExtent()
         }