make peace with LWPCookieJar

LWPCookieJar's domain handling is buggy:
-- saving cookies
LWP jar throw err on save if .domain is None,only accept ""
also throw error if .expires is None.
(but CookieJar works fine with None, and so many online reference use None rather than "")
-- loading cookies
LWP jar only set domain_specified=True for cookies with domain start with dot.(see _LWPCookieJar.py source)