py3: use unicodes in __slots__ __slots__ doesnot accepts bytes on Python 3.

merge with stable

url: fix crash by empty path with #fragments Before, "#foo" paths made hg crash. We've moved the #fragment parsing at 64fbd0de9773, but we shouldn't set path to None too early. This patch just removes the "if not path:" block since that's checked a few lines later.

py3: make i18n use encoding.environ