nullify these grids on exit so that we dont try to destroy them... which was raising errors when running tests on IE

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1552 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

tests/test_Layer_KaMap.html

@@ -67,6 +67,8 @@
         var testBounds = new OpenLayers.Bounds(1,2,3,4);
         
         t.ok( bounds.equals(testBounds), "getKaMapBounds() returns correct bounds")
+        
+        layer.grid = null;
     }
 
     function test_05_Layer_KaMap_getResolution(t) {
@@ -141,6 +143,8 @@
         t.eq( clone.tileSize.w, 500, "changing layer.tileSize does not change clone.tileSize -- a fresh copy was made, not just copied reference");
 
         t.eq( clone.alpha, layer.alpha, "alpha copied correctly");
+
+        layer.grid = null;
     }
 
     function test_11_Layer_KaMap_setMap(t) {