With review from elem, and oversight from tschaub, rolling in

SphericalMercator changes. Note that this explicitly does *not* include 
r4182 , so as to keep changes to a single logical set: that should be
filed in a seperate bug if it can be reproduced against trunk after this
commit. Hooray for Tim, thanks for all the feedback, onward and upward!
(Closes #686)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@4221 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Yahoo.js

@@ -57,6 +57,14 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
      * {YahooMapType}
      */
     type: null,
+    
+    /**
+     * APIProperty: sphericalMercator
+     * {Boolean} Should the map act as a mercator-projected map? This will
+     * cause all interactions with the map to be in the actual map projection,
+     * which allows support for vector drawing, overlaying other maps, etc. 
+     */
+    sphericalMercator: false, 
 
     /** 
      * Constructor: OpenLayers.Layer.Yahoo
@@ -69,6 +77,10 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
         OpenLayers.Layer.EventPane.prototype.initialize.apply(this, arguments);
         OpenLayers.Layer.FixedZoomLevels.prototype.initialize.apply(this, 
                                                                     arguments);
+        if(this.sphericalMercator) {
+            OpenLayers.Util.extend(this, OpenLayers.Layer.SphericalMercator);
+            this.initMercatorParameters();
+        }
     },
     
     /**
@@ -294,7 +306,9 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
      * {Float} Longitude of the given MapObject LonLat
      */
     getLongitudeFromMapObjectLonLat: function(moLonLat) {
-        return moLonLat.Lon;
+        return this.sphericalMercator ? 
+            this.forwardMercator(moLonLat.Lon, moLonLat.Lat).lon :
+            moLonLat.Lon;
     },
 
     /**
@@ -307,7 +321,9 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
      * {Float} Latitude of the given MapObject LonLat
      */
     getLatitudeFromMapObjectLonLat: function(moLonLat) {
-        return moLonLat.Lat;
+        return this.sphericalMercator ? 
+            this.forwardMercator(moLonLat.Lon, moLonLat.Lat).lat :
+            moLonLat.Lat;
     },
 
     /**
@@ -321,7 +337,14 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
      * {Object} MapObject LonLat built from lon and lat params
      */
     getMapObjectLonLatFromLonLat: function(lon, lat) {
-        return new YGeoPoint(lat, lon);
+        var yLatLong;
+        if(this.sphericalMercator) {
+            var lonlat = this.inverseMercator(lon, lat);
+            yLatLong = new YGeoPoint(lonlat.lat, lonlat.lon);
+        } else {
+            yLatLong = new YGeoPoint(lat, lon);
+        }
+        return yLatLong;
     },
 
   // Pixel