Restructure pkg/unittest and pkg/webdriver to follow the pub conventions.

tests/html/xsltprocessor_test.dart

-#library('XSLTProcessorTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library XSLTProcessorTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
 
   useHtmlConfiguration();
 
   var isXSLTProcessor =
       predicate((x) => x is XSLTProcessor, 'is an XSLTProcessor');
 
   test('constructorTest', () {
       var processor = new XSLTProcessor();
       expect(processor, isNotNull);
       expect(processor, isXSLTProcessor);
     });
 }