fixed find() bug

was calling selector_to_xpath() in the loop, breaking the selector after the second call.
fixed t/find.t test plan
Merge pull request #8 from cafe01/findmethodbug

fixed find() bug
Search from '//' when the node was created from HTML. ref. #8

This commit fixes:

  is wq('<html>1</html>')->find('html')->size, 1, 'find() includes root elements';
one more test case