routine.

Follow RFC2616 more closely, and make relative (ie: max-age) specifications
take precedence over absolute specifications (Expires:)

Add an explicit clock-skew window (parameter: clock_skew) and only
interpret Expires: in absolute terms if the Date: header is inside
this window.

Explicit check for the case where the backend sends an Expires: which
is before the Date:, even if the Date: is out side our window.




git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3019 d4fa192b-c00b-0410-8231-f00ffab90ce4