added support for text labels. This also adds getCentroid methods to all

geometries. Thanks crschmidt for the great help with this patch, and 
thanks to camptocamp for the initial work on this and rcoup for creating 
the first patches. r=crschmidt (closes #1895)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9262 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Geometry.js

@@ -224,6 +224,17 @@ OpenLayers.Geometry = OpenLayers.Class({
         //
         return 0.0;
     },
+    
+    /**
+     * APIMethod: getCentroid
+     * Calculate the centroid of this geometry. This method is defined in subclasses.
+     *
+     * Returns:
+     * {<OpenLayers.Geometry.Point>} The centroid of the collection
+     */
+    getCentroid: function() {
+        return null;
+    },
 
     /**
      * Method: toString