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/Map.js

@@ -238,6 +238,15 @@ OpenLayers.Map = OpenLayers.Class({
      *          stylesheets or style declarations directly in your page.
      */
     theme: null,
+    
+    /** 
+     * APIProperty: displayProjection
+     * {<OpenLayers.Projection>} Requires proj4js support.Projection used by
+     *     several controls to display data to user. If this property is set,
+     *     it will be set on any control which has a null displayProjection
+     *     property at the time the control is added to the map. 
+     */
+    displayProjection: null,
 
     /**
      * APIProperty: fallThrough
@@ -915,6 +924,13 @@ OpenLayers.Map = OpenLayers.Class({
         // If a control doesn't have a div at this point, it belongs in the
         // viewport.
         control.outsideViewport = (control.div != null);
+        
+        // If the map has a displayProjection, and the control doesn't, set 
+        // the display projection.
+        if (this.displayProjection && !control.displayProjection) {
+            control.displayProjection = this.displayProjection;
+        }    
+        
         control.setMap(this);
         var div = control.draw(px);
         if (div) {