Treat Expires: <not RFC1123> as 0

Per RFC2616, section 14.21:

"HTTP/1.1 clients and caches MUST treat other invalid date formats,
especially including the value "0", as in the past (i.e., "already
expired")."

So if you see a Date header but you can't parse it you should return 0
not -1 from getExpiresTime. Unless parseRfc1123Date always returns
zero for dates it can't parse in which case you're already set.

Thanks to Bryan McQuade for pointing this out.

[zhoresh, 2010-03-24 21:34:56]

LGTM