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

lib/OpenLayers/Control/MousePosition.js

@@ -51,6 +51,13 @@ OpenLayers.Control.MousePosition = OpenLayers.Class(OpenLayers.Control, {
      * {<OpenLayers.LonLat>}
      */
     lastXy: null,
+
+    /**
+     * APIProperty: displayProjection
+     * {<OpenLayers.Projection>} A projection that the 
+     * mousecontrol will display.
+     */
+    displayProjection: null, 
     
     /**
      * Constructor: OpenLayers.Control.MousePosition
@@ -113,7 +120,12 @@ OpenLayers.Control.MousePosition = OpenLayers.Class(OpenLayers.Control, {
                 // map has not yet been properly initialized
                 return;
             }    
+            if (this.displayProjection) {
+                lonLat.transform(this.map.getProjectionObject(), 
+                                 this.displayProjection );
+            }      
             this.lastXy = evt.xy;
+            
         }
         
         var digits = parseInt(this.numdigits);