Windows: add test for path.normalize with UNC paths

test/simple/test-path.js

@@ -197,6 +197,8 @@ if (isWindows) {
   assert.equal(path.normalize('a//b//../b'), 'a\\b');
   assert.equal(path.normalize('a//b//./c'), 'a\\b\\c');
   assert.equal(path.normalize('a//b//.'), 'a\\b');
+  assert.equal(path.normalize('//server/share/dir/file.ext'),
+               '\\\\server\\share\\dir\\file.ext');
 } else {
   assert.equal(path.normalize('./fixtures///b/../b/c.js'),
                'fixtures/b/c.js');