Removing imageOffset and using getImageSize.

This fixes a regression that was introduced with the Tile.Image overhaul. See http://trac.osgeo.org/openlayers/ticket/3625.

lib/OpenLayers/Layer.js

@@ -159,13 +159,6 @@ OpenLayers.Layer = OpenLayers.Class({
      */
     imageSize: null,
     
-    /**
-     * Property: imageOffset
-     * {<OpenLayers.Pixel>} For layers with a gutter, the image offset 
-     *     represents displacement due to the gutter.
-     */
-    imageOffset: null,
-
   // OPTIONS
 
     /** 
@@ -693,7 +686,7 @@ OpenLayers.Layer = OpenLayers.Class({
     /**
      * APIMethod: setTileSize
      * Set the tile size based on the map size.  This also sets layer.imageSize
-     *     and layer.imageOffset for use by Tile.Image.
+     *     or use by Tile.Image.
      * 
      * Parameters:
      * size - {<OpenLayers.Size>}
@@ -710,8 +703,6 @@ OpenLayers.Layer = OpenLayers.Class({
           //                              this.name + ": layers with " +
           //                              "gutters need non-null tile sizes");
           //}
-            this.imageOffset = new OpenLayers.Pixel(-this.gutter, 
-                                                    -this.gutter); 
             this.imageSize = new OpenLayers.Size(tileSize.w + (2*this.gutter), 
                                                  tileSize.h + (2*this.gutter)); 
         }