avoid double redraw when panning/zooming. p=tsauerwein,r=erilem (closes #2801)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@10863 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

tests/Renderer/Canvas.html

@@ -23,7 +23,7 @@
         
         var extent = new OpenLayers.Bounds(1,2,3,4);
         r.resolution = 1;
-        r.setExtent(extent);
+        r.setExtent(extent, true);
         t.ok(r.extent.equals(extent), "extent is correctly set");
         t.eq(r.resolution, null, "resolution nullified");
     }