4or whatever reason, the 'singleFile' property was never properly documented on grid

git-svn-id: http://svn.openlayers.org/trunk/openlayers@3900 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -28,6 +28,15 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      */
     grid: null,
 
+    /**
+     * APIProperty: singleTile
+     * {Boolean} Moves the layer into single-tile mode, meaning that one tile 
+     *     will be loaded. The tile's size will be determined by the 'ratio'
+     *     property. When the tile is dragged such that it does not cover the 
+     *     entire viewport, it is reloaded.
+     */
+    singleTile: false,
+
     /** APIProperty: ratio
      *  {Float} Used only when in single-tile mode, this specifies the 
      *          ratio of the size of the single tile to the size of the map.