Move unittest from lib to pkg.

tests/html/instance_of_test.dart

 #library('InstanceOfTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   CanvasElement canvas;
 
   canvas = new Element.tag('canvas');
   canvas.attributes['width'] = 100;
   canvas.attributes['height'] = 100;
   document.body.nodes.add(canvas);
 
@@ skipping 32 matching lines @@
     Expect.isFalse(bytes is CanvasElement);
     Expect.isFalse(bytes is ImageData);
     Expect.isTrue(bytes is Uint8ClampedArray);
 
     // FIXME: Ensure this is an SpanElement when we next update
     // WebKit IDL.
     var span = new Element.tag('span');
     Expect.isTrue(span is Element);
   });
 }