Default the buffer to 0 instead of 2. On small maps (or fullscreen

maps on small devices) this is a huge win: instead of downloading
*42 tiles* on a 500x500 div, we now download just 12, a 3.5x savings
in downloads by default. The buffer of 2 was originally chosen when
most maps were based on slow-loading WMS laeyrs and having an area
to pan into was more important. That default no longer makes sense.

(Closes #3111) r=tschaub


git-svn-id: http://svn.openlayers.org/trunk/openlayers@11481 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -78,8 +78,11 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      * {Integer} Used only when in gridded mode, this specifies the number of 
      *           extra rows and colums of tiles on each side which will
      *           surround the minimum grid tiles to cover the map.
+     *           For very slow loading layers, a larger value may increase
+     *           performance somewhat when dragging, but will increase bandwidth
+     *           use significantly. 
      */
-    buffer: 2,
+    buffer: 0,
 
     /**
      * APIProperty: numLoadingTiles