Documenting that OSM extends XYZ and XYZ extends Grid. The buffer property comes from the Grid prototype. (closes #2766)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@10561 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/XYZ.js

@@ -11,6 +11,9 @@
  * Class: OpenLayers.Layer.XYZ
  * The XYZ class is designed to make it easier for people who have tiles
  * arranged by a standard XYZ grid. 
+ * 
+ * Inherits from:
+ *  - <OpenLayers.Layer.Grid>
  */
 OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
     
@@ -159,8 +162,10 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
  * (end)
  *
  * This layer defaults to Spherical Mercator.
+ * 
+ * Inherits from:
+ *  - <OpenLayers.Layer.XYZ>
  */
-
 OpenLayers.Layer.OSM = OpenLayers.Class(OpenLayers.Layer.XYZ, {
      name: "OpenStreetMap",
      attribution: "Data CC-By-SA by <a href='http://openstreetmap.org/'>OpenStreetMap</a>",