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

tests/Layer/TMS.html

@@ -134,7 +134,7 @@
         t.plan(1);
             m = new OpenLayers.Map("map", {'maxExtent':new OpenLayers.Bounds(-122.6579,37.4901,-122.0738,37.8795)});
             layer = new OpenLayers.Layer.TMS( "TMS", 
-                    "http://labs.metacarta.com/wms-c/Basic.py/", {layername: 'basic', type:'png', resolutions:[0.000634956337608418]} );
+                    "http://labs.metacarta.com/wms-c/Basic.py/", {layername: 'basic', type:'png', resolutions:[0.000634956337608418], buffer: 2} );
             m.addLayer(layer);
             m.zoomToMaxExtent();
             t.eq(layer.getURL(layer.grid[3][3].bounds), "http://labs.metacarta.com/wms-c/Basic.py/1.0.0/basic/0/1/1.png", "TMS tiles around rounded properly.");